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ELEMENTS  OF 
STEAM  AND  GAS  POWER  ENGINEERING 


VMeQraw-M  Bock  (h.  Jne 

PUBLISHERS     OP     BOOKS     FOlO 

Electrical  World  t  Engineering  News-Record 
Power  v  Engineering  and  Mining  Journal-Press 
Chemical  and  "Metallurgical  Engineering 
Electric  Railway  Journal  ▼  Coal  Age 
American  "Machinist v  Ingenieria  Internacional 
Hectrical  Merchandising  ▼  BusTransportation 
Journal  of  Electricity  and  Western  Industry 
Industrial  Engineer 


« 

V 


><J 


ELEMENTS    OF 

STEAM  AND  GAS  POWEE 
ENGINEERING 


BY 
ANDREY   A.    POTTER 

DEAN    OF    ENGINEERING,   PURDUE    UNIVERSITY,    FORMERLY    DEAN    OF    ENGINEERING, 

KANSAS   STATE    AGRICULTURAL   COLLEGE.      AUTHOR    OF    "FARM    MOTORS", 

ENGINEERING    THERMODYNAMICS,    ETC. 

AND 


JAMES  P.  CALDERWOOD 

PROFESSOR   OF   MECHANICAL   ENGINEERING   IN   THE    KANSAS   STATE   AGRICULTURAL 
COLLEGE.      AUTHOR    OF    ENGINEERING    THERMODYNAMICS,    ETC. 


First  Edition 
Fourth  Impression 


McGRAW-HILL  BOOK  COMPANY,  Inc. 
NEW  YORK:  370  SEVENTH  AVENUE 

LONDON :  6  &  8  BOUVERIE  ST.,  E.  C.  4 

BSD.  OBuARr 


Copyright,  1920,  by  the 
McGraw-Hill  Book  Company,  Inc. 


XHE  MAPLE  PRESS  YORK:  PA 


PREFACE 

In  the  preparation  of  this  treatise  the  authors  have  attempted 
to  present  a  clear  and  concrete  statement  of  the  principles  under- 
lying the  construction  and  operation  of  steam  and  gas  power 
equipment. 

The  first  chapter  is  devoted  to  a  general  survey  of  the  field 
of  power  engineering  and  brings  out  the  factors  essential  for  the 
production  of  power,  the  principles  governing  the  action  of 
various  mechanical  motors,  and  a  comparison  of  their 
performance. 

The  main  portion  of  the  book  is  divided  into  three  parts. 
The  first  part  takes  up  the  subject  of  steam  power  and  includes 
fuels,  combustion,  theory  of  steam  generation,  boilers,  boiler 
auxiliaries,  boiler  accessories,  steam  engines,  steam  turbines, 
auxiliaries  for  steam  engines  and  turbines,  and  the  testing  of 
steam  power  equipment.  The  second  part  is  devoted  to  gas 
power  and  includes  a  study  of  the  internal  combustion  engine, 
fuels  for  internal  combustion  engines,  gas  producers  and  the 
various  auxiliaries  found  in  connection  with  internal  combustion 
engine  power  plants.  The  last  portion  of  the  book  treats  of  the 
application  of  steam  and  gas  power  to  locomotives,  automobiles, 
trucks  and  tractors. 

The  method  followed  in  each  chapter  was  to  give:  first, 
the  fundamental  principles  underlying  the  particular  phase  of 
equipment  under  consideration;  second,  the  structural  details; 
third,  auxiliary  parts;  fourth,  operation  and  management  of  the 
equipment  considered. 

This  book  has  been  prepared  primarily  as  a  textbook  for 
students  in  engineering  schools  and  colleges  in  order  to  familiarize 
them  with  power  plant  equipment  before  they  take  up  the  more 
abstract  study  of  thermodynamics  and  design.  The  subject 
matter  of  this  treatise  is  so  prepared  that  it  should  prove  of 
considerable  value  to  those  who  are  responsible  for  the  operation 
of  steam  or  internal  combustion  engine  power  plants.     Illustrative 


***-> 


vi  PREFACE 

problems  will  be  found  at  the  close  of  each  chapter.  These 
problems  are  intended  mainly  as  a  guide  in  encouraging  outside 
reference  reading. 

In  the  preparation  of  this  text  the  authors  are  particularly 
indebted  to  H.  W.  Davis  and  A.  J.  Mack  of  the  Kansas  State 
Agricultural  College  for  their  valuable  assistance. 

The  authors  are  also  grateful  to  E.  M.  Shealy,  J.  A.  Moyer, 
A.  J.  Wood,  C.  F.  Gebhardt,  L.  H.  Morrison,  R.  H.  Fernald, 
G.  A.  Orrok,  and  A.  M.  Greene  for  their  permission  to  use  certain 
illustrations  from  publications  of  which  they  are  authors.  The 
various  manufacturers  of  power  machinery  have  also  been  most 
liberal  in  giving  the  authors  permission  to  use  cuts. 

Andrey  A.  Potter. 
James  P.  Calderwood. 
Manhattan,  Kansas, 
January,    1920. 


&  *Vtf 


CONTENTS 


Page 
Preface  .    .    .    . v 

CHAPTER  I 

Fundamentals  of  Power  Engineering 1 

Mechanical  Power — Factors  Essential  for  the  Production  of 
Power — Sources  of  Energy — Principles  Governing  the  Action  of 
Various  Mechanical  Motors — Comparison  of  Various  Types  of 
Motors — Principal  Parts  of  a  Steam  Power  Plant — Condensing 
Steam  Power  Plant — Gas  Power  Plants — Problems. 

CHAPTER  II 

Steam  Power  Fuels  and  Combustion 10 

Fuels.  The  Heating  Value  of  Fuels — The  Proximate  Analysis 
of  Fuels — Fuels  for  Steam  Generation. 

Combustion.     Chemistry  of  Combustion — Air  Required  for  Com- 
bustion— Flue  Gas  Analysis. 
Problems. 

CHAPTER  III 

Steam 21 

Theory  of  Steam  Generation — Quality  of  Steam — Steam  Tables — 
Determination  of  the  Quality  of  Steam — Problems. 

CHAPTER  IV 

Boilers 35 

Classification  of  Boilers — Plain  Cylindrical  Boiler — Horizontal 
Return  Tubular  Boiler — Scotch  Marine  Boiler — Locomotive  Boiler 
— Vertical  Fire  Tube  Boiler — Water  Tube  Boilers — Babcock  and 
Wilcox  Boiler — Heine  Boiler — Stirling  Boiler — Wickes  Boiler 
— Parker  Down  Flow  Boiler — Marine  Water  Tube  Boilers — 
Materials — Heating  Surface — Staying — Settings  and  Furnaces 
— Capacity  and  Efficiency  of  Steam  Boilers — Firing — Management 
of  Boilers — Problems. 

CHAPTER  V 

Boiler  Auxiliaries 58 

Superheaters.  Types  of  Superheaters — Babcock  and  Wilcox 
Superheater — Stirling  Superheater — Heine  Superheater — Foster 
Superheater. 

vii 


viii  CONTENTS 

Page 

Mechanical  Stokers.  The  Field  of  Mechanical  Stokers — Chain- 
grate  Stokers — Inclined  Grate  Stokers — Under-feed  Stokers — 
Taylor  Stoker. 

Feed  Water  Heaters  and  Economizers.  Feed  Water  Heaters — 
Economizers. 

Draft  Producing  Equipment.     Chimneys — Artificial  Draft. 
Feed   Pumps   and   Injectors.     Feed    Pumps — Injectors — Duty   of 
Pumps. 

Grates  for  Boiler  Furnaces. 
Coal  and  Ash  Handlinq  Systems. 
Problems. 

CHAPTER  VI 

Piping  and  Boiler  Room  Accessories 83 

Grades  and  Sizes  of  Piping — Pipe  Fittings — Expansion  of  Piping — 
Pipe  Covering — Erecting  Pipe — Valves — Blow-off  Valves — Safety 
Valves — Steam  Gages — Water  Glass  and  Gage  Cocks — Water 
Column — Steam  Traps — Fusible  Plugs — Problems. 

CHAPTER  VII 

Steam  Engines 92 

Description  of  the  Steam  Engine — Early  History  of  the  Steam 
Engine — Losses  in  Steam  Engines — Action  of  the  Plain  Slide  Valve 
— Types  of  Plain  Slide  Valves — Balanced  Valves — The  Double 
Ported  Valve — The  Corliss  Engine — Poppet  Valves — The  Uniflow 
Steam  Engine — Reversing  Engines — Condensing  and  Non-Con- 
densing Engines — Multiple  Expansion  Engines — The  Steam  Loco- 
mobile— Valve  Setting — Setting  Corliss  Valves — Horsepower 
— Indicated  Horsepower — Indicator  Reducing  Motions — The 
Indicator  Card — The  Measurement  of  Power  from  Indicator 
Cards — Valve  Setting  by  Indicator  Cards — Brake  Horsepower 
— Friction  Horsepower — Mechanical  Efficiency — Steam  Engine 
Governors — Engine  Details — Lubricators — Steam  Engine  Econ- 
omy— Installation  and  Care  of  Steam  Engines — Problems. 

CHAPTER  VIII 

Steam  Turbines 135 

Advantages  of  the  Steam  Turbine — History  of  the  Steam  Turbine 
The  DeLaval  Simple  Impulse  Steam  Turbine — Velocity  and  Energy 
of  Steam — Compound  Impulse  Turbines — The  Rateau  Turbine — 
The  Kerr  Turbine — The  DeLaval  Multiple  Impulse  Turbine — 
The   Terry    Turbine— The    Sturtevant    Turbine— The    Westing- 


CONTENTS  ix 

Page 
house  Impulse  Turbine — The  Curtis  Steam  Turbine — The  Reaction 
Turbine — The  Parsons  Turbine — The  Impulse-Reaction  Turbine — 
The  Spiro  Steam  Turbine — Exhaust  Steam  Turbines — Applications 
of  the  Steam  Turbine — Steam  Turbine  Economy — Installation  and 
Care  of  Steam  Turbines — Problems. 

CHAPTER  IX 

Engine  and  Turbine  Auxiliaries 164 

Condensers.     The  Principle  of  the  Condenser — The  Measurement 

of  Vacuum — Types  of  Condensers — Jet  Condensers — Barometric 

Condensers — Ejector  Condensers — Surface  Condensers. 

Vacuum  Pumps.     Wet  Air  Pumps — Edwards  Air  Pump — Dry  Air 

Pumps — Circulating  Pumps. 

Cooling  Ponds  and  Cooling  Towers.     Reclaiming  Cooling  Water — 

Cooling  Ponds — Spray  Ponds — Cooling  Towers. 

Separators.     Steam  Separators — Exhaust  Steam  and  Oil  Separators 

— Exhaust  Heads. 

Problems. 

CHAPTER  X 

Steam  Power  Plant  Testing 182 

General  Rules — Preparing  for  the  Test — Starting  and  Stopping 
the  Test — Weighing  the  Fuel — Weighing  the  Feed  Water — Draft 
Gages — Temperature  Measurement — Measuring  the  Weight  of 
Steam — Measurement  of  Power — Measurement  of  Speed — In- 
dicator and  Calorimeters — A.  S.  M.  E.  Code — Problems. 


CHAPTER  XI 

Internal  Combustion  Engines 191 

History — The  Otto  Internal  Combustion  Engine  Cycle — The  Two- 
stroke  Cycle  Engine — The  Diesel  Internal  Combustion  Engine 
Cycle — Details  of  Internal  Combustion  Engines — Oil  Engines — 
Losses  in  Internal  Combustion  Engines — Installation  and  Care  of 
Internal  Combustion  Engines — Problems. 

CHAPTER  XII 

Internal  Combustion  Engine  Fuels  and  Gas  Producers 211 

Fuels.  Classification  of  Fuels — The  Heating  Value  of  a  Fuel — 
Selection  of  a  Fuel — Distillates  of  Crude  Petroleum — Gasoline — 
Kerosene — Crude  Oil — Alcohol — Benzol — Shale  Oil — Fuel  Gases — 
Blast-furnace  Gas — Coke-oven  Gas — Natural  Gas — Producer  Gas. 
Gas  Producers.     Details  of  Gas  Producers — Classification  of  Gas 


x  CONTENTS 

Page 
Producers — Suction   Gas   Producers — Pressure    Gas    Producers — 
Combination    Producers — Rating     of     Gas     Producers — Factors 
Influencing  Producer  Operation. 
Problems. 

CHAPTER  XIII 

Auxiliaries  for  Internal  Combustion  Engines 228 

Carburetors.  Principles  of  Carburetion — Carburetors — Simple  Car- 
buretors or  Mixed  Valves — Float  Feed  Carburetors — Kingston 
Carburetor — Marvel  Carburetor — Stewart  Carburetor — Stromberg 
Carburetor — Zenith  Carburetor — Holly  Carburetor — Kerosene 
Carburetors. 

Ignition  Systems.  Electric  Ignition  Systems — The  Make-and- 
Break  System  of  Ignition — The  Jump  Spark  System  of  Ignition — 
Comparison  of  the  Two  Systems  of  Electric  Ignition — Source  of 
Current — Electric  Batteries — Primary  Batteries — Storage  Batteries 
— The  Lead  Storage  Battery — The  Edison  or  Nickel-Iron  Storage 
Battery — Ignition  Dynamos — Magnetos — Low  Tension  Magnetos 
— Inductor  Type  of  Magneto — High  Tension  Magnetos — Timer 
and  Distributor  Systems. 

Governors.     Hit-and-Miss  Governing — Quality  Governing — Quan- 
tity Governing — Combination  Systems. 
Mufflers. 
Problems. 

CHAPTER  XIV 

Gas  Power  Plant  Testing ,    .    .   255 

Measurement  of  Fuel  Used — Heat  Consumption  of  the  Engine — 
Brake  Horsepower — Indicated  Horsepower — The  Measurement 
of  the  Heat  Absorbed  by  the  Jacket  Water — Duration  of  Test — 
Starting  the  Test — Gas  Producer  Testing — A.  S.  M.  E.  Code — 
Problems. 

CIJAPTER  XV 

Locomotives 260 

The  Locomotive  Compared  with  the  Stationary  Steam  Power  Plant 
— The  Essential  Parts  of  a  Locomotive — Early  History  of  the 
Locomotive — Classification  of  the  Locomotive — The  Development 
of  the  Locomotive — The  Mallet  Articulated  Compound  Locomotive 
Superheaters — Locomotive  Stokers — Draft  Appliances — Injectors 
— Air  Brakes — Problems. 


CONTENTS  xi 

Page 
CHAPTER  XVI 

Automobiles,  Trucks  and  Tractors 273 

Automobiles.  Types  of  Automobiles — Essential  Parts  of  a  Gasoline 
Automobile— Automobile  Motors — Cooling  of  Automobile  Motors- 
Lubrication — Automobile  Valves — Clutches — Transmissions — Dif- 
ferentials for  Automobiles — Universal  Joint — Front  and  Rear- Axles 
— Steering  and  Control  Systems — Brakes — Wheels  and  Tires — Car- 
buretors— Ignition — Automobile  Starting  Systems — Automobile 
Lighting — Management  of  Automobiles. 

Trucks.  Power  Plants  for  Trucks — Power  Transmission  Systems 
for  Trucks. 

Tractors.  Essential  Parts  of  a  Tractor — Steam  Tractors — Gas 
Tractors — Rating  of  Tractors — Care  of  Trucks  and  Tractors. 
Problems. 

Index 299 


ELEMENTS  OF  STEAM 

AND 

GAS  POWER  ENGINEERING 


CHAPTER  I 
FUNDAMENTALS  OF  POWER  ENGINEERING 

Mechanical  Power. — The  substitution  of  mechanical  power  for 
animal  labor  marks  a  most  important  epoch  in  the  progress  of 
civilization.  The  increase  in  the  amount  of  mechanical  power 
used  for  manufacturing,  for  transportation,  and  for  other  pur- 
poses has  been  enormous  during  the  past  forty  years  and  particu- 
larly so  in  the  United  States  of  America.  The  greatest  factors 
which  contributed  to  the  increased  use  of  power  are  the  develop- 
ment of  electrical  machinery  and  efficient  electrical  transmission 
systems,  the  perfection  of  the  internal  combustion  engine  and 
steam  turbine,  the  growth  of  the  manufacturing  industries,  and 
the  improvements  in  transportation  equipment  and  systems. 

Factors  Essential  for  the  Production  of  Power. — Two  require- 
ments are  essential  for  the  production  of  power:  first,  a  source 
from  which  energy  may  be  derived ;  and  second,  a  motor  which  is 
capable  of  transforming  this  energy  into  work.  Without  energy 
all  attempts  to  produce  power  would  be  futile;  without  a  motor 
energy  cannot  be  utilized,  even  when  available,  in  producing 
power. 

A  motor  is  an  apparatus  capable  of  transforming  energy  into 
mechanical  work.  Any  apparatus  which  transforms  energy 
from  one  form  into  another,  but  not  into  work,  is  not  a  motor. 

1 


2  STEAM  AND  GAS  POWER  ENGINEERING 

A  Motor  Must  Do  Work.  By  work  is  meant  the  production 
of  motion  against  some  external  force.  The  mechanical  motors 
available  for  the  production  of  power  are  heat  engines,  including 
steam,  gas,  oil,  hot-air,  and  solar  engines;  pressure  engines,  such 
as  water  wheels  and  water  motors;  windmills;  electric  motors. 

Sources  of  Energy. — The  principal  source  of  all  energy  is  the 
sun.  It  causes  the  growth  of  plants  which  furnish  food  for  man 
and  animals.  The  great  coal  deposits  are  only  the  result  of  the 
storing  up  of  the  sun's  rays  in  plants  in  bygone  days.  These 
rays  are  also  responsible  for  the  raising  of  water  from  sea  level  to 
mountain  top,  thus  giving  it  energy  which  can  be  utilized  to  turn 
water  wheels  and  do  useful  work. 

On  the  other  hand,  while  the  sun's  rays  are  the  fundamental 
source  of  all  energy,  they  can  be  utilized  directly  by  man  only  to 
a  very  limited  extent.  Heat  engines  have  been  built  which 
transform  the  heat  derived  directly  from  the  sun  into  mechanical 
energy;  but,  because  of  their  bulk  when  compared  with  the  energy 
transformed  and  because  of  the  irregularities  in  the  sun's  rays 
caused  by  clouds  and  the  movement  of  the  earth,  this  type 
of  motor  has  never  proved  practicable.  As  a  result,  secondary 
sources  of  energy  must  be  utilized.  These  secondary  sources 
are:  the  wind;  waterfalls;  carbon  in  different  forms,  such  as  coal, 
petroleum,  or  gas;  and  chemicals  such  as  are  used  in  electric 
batteries. 

Principles  Governing  the  Action  of  Various  Mechanical 
Motors. — All  mechanical  motors  do  work  by  virtue  of  motion 
given  to  a  piston,  or  to  blades  on  a  wheel  by  some  substance  such 
as  water,  steam,  gas,  or  air;  or  to  a  rotor  by  electricity.  The 
first  requirement  in  any  of  these  cases  is  that  the  above-men- 
tioned substance,  often  called  the  working  substance,  be  under 
considerable  pressure. 

This  pressure  in  the  case  of  the  water  motor  or  waterwheel  is 
obtained  by  collecting  water  in  dams  and  tanks,  or  by  utilizing 
the  kinetic  energy  of  natural  waterfalls.  The  total  power 
available  in  water  when  in  motion  depends  on  the  weight  of 
water  discharged  in  a  given  time  and  on  the  head  or  distance 
through  which  the  water  is  allowed  to  fall.  The  head  of  water 
can  be  utilized  by  its  weight  or  pressure  acting  directly  either  on 
a  piston,  or  on  blades  or  paddles  on  wheels. 


FUNDAMENTALS  OF  POWER  ENGINEERING        3 

Considering  next  the  various  forms  of  heat  engines,  we  find 
work  accomplished  by  steam  or  gas  under  pressure,  the  pressure 
being  obtained  by  utilizing  the  heat  of  some  fuel  or  of  the  rays 
of  the  sun. 

A  motor  utilizing  the  heat  of  the  sun  is  called  a  solar  motor  or  a 
solar  engine.  The  action  of  this  type  of  motor  depends  on  the 
vaporization  of  water  into  steam  by  means  of  the  rays  of  the  sun, 
which  are  concentrated  and  intensified  by  means  of  reflecting 
surfaces.  The  steam  thus  generated  is  used  in  some  form  of  heat 
motor. 

In  the  case  of  the  steam  power  plant  (Fig.  1,  page  6)  a  fuel, 
like  coal,  oil,  or  gas,  is  burned  in  a  furnace  and  its  heat  of  com- 
bustion is  utilized  in  changing  water  into  steam  at  high  pressure 
in  a  special  vessel  called  a  boiler.  This  high-pressure  steam  is 
then  conveyed  by  pipes  to  the  engine  cylinder  where  its  energy 
is  expended  in  pushing  a  piston  as  in  the  case  of  the  reciprocating 
engine.  The  sliding  motion  of  the  piston  may  be  changed  into 
rotary  motion  at  the  shaft  by  the  interposition  of  a  connecting 
rod  and  crank.  Another  method  is  to  allow  the  high-pressure 
steam  to  escape  through  a  nozzle,  strike  blades  on  a  wheel  and 
produce  rotary  motion  direct,  as  in  the  case  of  the  steam  turbine 
(Fig.  109,  page  135). 

In  another  type  of  heat  engine,  called  a  hot-air  engine,  air  is 
heated  in  the  engine  cylinder  by  a  fuel  which  is  burned  outside 
of  the  cylinder.  The  air  by  its  expansion  drives  a  piston  and 
does  work. 

In  the  case  of  gas  and  oil  engines  (Fig.  163,  page  194),  the  fuel 
which  must  be  in  a  gaseous  form  as  it  enters  the  engine  cylinder, 
is  mixed  with  air  in  the  proper  proportions  to  form  an  explosive 
mixture.  It  is  then  compressed  and  ignited  within  the  cylinder 
of  the  engine,  the  high  pressure  produced  by  the  explosion  push- 
ing on  a  piston  and  doing  work.  These  engines  belong  to  a  class  f 
called  internal-combustion  engines,  and  differ  from  the  steam  and 
hot-air  engines,  which  are  sometimes  called  external-combustion 
engines,  in  that  the  fuel  is  burned  inside  the  engine  cylinder,  in- 
stead of  in  an  auxiliary  apparatus. 

The  windmill  derives  its  high  pressure  for  doing  work  from  the 
moving  atmosphere. 

The  electric  motor  converts  electrical  energy  at  high  pressure 


4  STEAM  AND  GAS  POWER  ENGINEERING 

into  work;  this  electrical  pressure  or  voltage  is  produced  in  an 
apparatus  called  an  electrical  dynamo,  or  a  generator  of  electricity. 

Comparison  of  Various  Types  of  Motors. — The  solar  motor,  as 
previously  stated,  is  but  little  used  on  account  of  its  high  first 
cost  and  great  bulk  in  relation  to  the  small  power  developed. 

In  localities  where  the  wind  is  abundant  and  little  power  is 
needed,  the  windmill  is  a  desirable  and  cheap  source  of  power. 
The  greatest  application  of  windmills  is  for  the  pumping  of 
water  for  residences  and  farms,  and  for  such  other  work  as  does 
not  suffer  from  suspension  during  calm  weather.  Electric  storage 
and  lighting  on  a  small  scale  from  the  power  of  a  windmill  has 
been  tried  in  several  places  with  fair  success,  but  probably  will 
not  be  adopted  to  any  great  extent  on  account  of  the  high  first 
cost  and  the  small  practical  capacity  of  such  an  installation. 

The  water  motor  or  water  turbine  is  very  economical  if  a 
plentiful  supply  of  water  can  be  had  at  a  fairly  high  head,  but 
its  reliability  is  affected  by  drought,  floods,  and  ice  in  the  water 
supply.  For  this  reason  many  of  the  hydraulic  power  stations 
must  resort  to  the  use  of  steam  or  gas  power  during  certain 
seasons  of  the  year. 

The  hot-air  engine,  while  not  economical  in  fuel  consumption, 
is  used  to  a  limited  extent  for  pumping  water  in  places  where  the 
cost  of  fuel  is  not  an  important  item  and  where  safety  and  sim- 
plicity of  mechanism  are  essential.  The  hot-air  engine,  on  ac- 
count of  its  high  cost,  bulk,  and  poor  fuel  economy,  has  been 
largely  superseded  by  the  oil  engine,  which  uses  gasoline  or  the 
heavier  oils. 

The  internal-combustion  engine  (Chapter  XI),  whether  using 
gas  or  oil,  is  well  adapted  for  small  and  medium-sized  powers. 
It  finds  its  greatest  application  in  the  automobile  and  in  other 
power  vehicles  (Chapter  XVI) ;  also  for  uses  on  farms  either  as 
stationary  engines  or  as  oil  traction  engines. 

For  the  generation  of  electricity,  especially  in  large  units,  the 
steam  engine  (Chapter  VII)  and  the  steam  turbine  (Chapter  VIII) 
have  been  found  to  be  the  most  suitable  types  of  motors,  because 
of  their  lower  first  cost,  when  compared  with  other  types  of 
motors,  and  because  of  their  greater  reliability.  By  far  the  great- 
est part  of  commercial  power  is  developed  by  steam  motors. 
The  reason  for  this  fact  is  that  the  conversion  of  power  from  one 


FUNDAMENTALS  OF  POWER  ENGINEERING        5 

form  into  another  is  always  accompanied  by  losses;  thus  power 
developed  from  a  cheap  source  is  not  necessarily  the  most  eco- 
nomical from  a  commercial  point  of  view.  An  example  of  this  is 
the  hydro-electric  plant,  where  the  cost  of  power  would  be  small 
if  no  consideration  had  to  be  taken  of  the  greater  first  cost  of  the 
installation  and  the  cost  of  the  long  transmission  lines.  As 
another  illustration,  the  oil  engine  is  conceded  to  have  the  highest 
efficiency  as  a  motor  for  the  transforming  of  heat  energy  into 
work,  but  commercially  its  application  has  been  limited  to  special 
uses  or  to  those  localities  in  which  the  cost  of  oil  is  low  and  the 
supply  is  large.  When  all  factors  are  considered,  it  is  usually 
found  that  the  steam  power  plant  is  the  cheapest  producer  of 
power  in  large  quantities. 

About  three-fourths  of  the  total  power  used  for  manufacturing 
in  this  country  is  developed  by  steam  prime  movers;  that  is  by 
steam  engines  and  steam  turbines.  In  electric  generating  sta- 
tions over  70  per  cent,  of  the  power  is  developed  by  steam  prime 
movers  and  but  slightly  more  than  1  per  cent,  by  internal  com- 
bustion engines.  The  power  developed  by  gas  and  oil  engines 
in  connection  with  the  manufacturing  industries  is  less  than  5  per 
cent. 

Principal  Parts  of  a  Steam  Power  Plant. — The  principal  parts 
of  a  simple  steam  power  plant  are  illustrated  in  Fig.  1,  and  include 
the  following: 

1.  A  furnace,  in  which  the  fuel  is  burned.  This  consists  of  a 
chamber  arranged  with  a  grate  (1),  if  coal  or  any  other  solid  fuel 
is  used,  and  with  burners  when  the  fuel  is  in  the  liquid  or  gaseous 
state.  The  furnace  is  connected  through  a  flue  or  breeching  (2) 
to  a  chimney.  The  function  of  a  chimney  is  to  produce  sufficient 
draft,  so  that  the  fuel  will  have  the  proper  amount  of  air  for 
combustion;  it  also  serves  to  carry  off  the  obnoxious  gases  after 
the  combustion  process  is  completed.  The  flue  leading  to  the 
chimney  is  provided  with  a  damper  (3),  so  that  the  intensity  of 
the  draft  can  be  regulated. 

2.  A  boiler  (4),  which  is  a  closed  metallic  vessel  filled  to  about 
two-thirds  of  its  volume  with  water.  The  heat  developed  by  the 
burning  of  the  fuel  in  the  furnace  is  utilized  in  converting  the 
water  contained  in  the  boiler  into  steam.  The  boiler  (4)  is 
arranged  with  a  water  column  (5)  to  show  the  water  level,  with 


6 


STEAM  AND  GAS  POWER  ENGINEERING 


a  safety  valve  (6)  to  prevent  the  pressure  from  rising  too  high, 
and  with  a  gage  (7)  to  indicate  the  steam  pressure. 

3.  The  function  of  a  setting,  which  is  the  term  usually  used  to 
designate  the  brick  work  which  surrounds  the  boiler,  is  to  provide 
correct  spaces  for  the  furnace,  combustion  chamber  and  ash-pit, 
to  prevent  air  from  entering  the  furnace  above  the  fuel  bed,  and 
to  decrease  the  heat  of  radiation  to  a  minimum.  In  some  power 
plants  the  setting  is  also  used  to  support  the  boiler  shell,  but  this 
is  poor  practice. 


Fig.  1. — Elementary  non-condensing  power  plant. 

4.  The  feed  pump  (8)  supplies  the  boiler  with  water  through 
the  feed  pipe  (9). 

5.  The  steam  lines  (10)  and  (11)  convey  steam  from  the  boiler 
to  the  engine  and  to  the  steam  end  of  the  pump  respectively. 

6.  In  the  engine  the  energy  of  the  steam  is  expended  in  doing 
work.  The  steam  enters  the  engine  cylinder  (12)  through  the 
valve  (13)  and  pushes  on  the  piston  (14).  The  sliding  motion 
of  the  piston,  which  is  transmitted  to  the  piston  rod  (15),  is 
changed  into  rotary  motion  at  the  shaft  (16)  by  means  of  a  con- 
necting rod  (17)  and  crank  (18). 


FUNDAMENTALS  OF  POWER  ENGINEERING 


8 


STEAM  AND  GAS  POWER  ENGINEERING 


7.  The  exhaust  pipe  (19)  conveys  the  used  steam  to  the  atmos- 
phere, or  to  some  use  where  its  heat  is  abstracted,  converting 
the  steam  back  into  water. 

Condensing  Steam  Power  Plant. — In  Fig.  2  is  illustrated  a 
condensing  steam  power  plant  with  water  tube  boilers.  The 
various  parts  are  numbered  to  correspond  with  similar  parts  in 
the  simple  power  plant  of  Fig.  1. 


Fig.  3. —  Modern  steam  power  plant. 

In  Fig.  3  is  illustrated  a  modern  steam  turbine  plant  equipped 
with  coal  and  ash  handling  machinery,  mechanical  stokers,  and 
other  labor  saving  devices. 

Gas  Power  Plants. — The  equipment  of  a  gas  power  plant  de- 
,  pends  upon  the  fuel  used.  The  simplest  type  of  gas  power  plant 
is  the  gasoline  engine  (Fig.  163),  which  consists  of  a  cylinder  and 


FUNDAMENTALS  OF  POWER  ENGINEERING        9 

piston,  a  carburetor  for  preparing  the  explosive  mixture,  valves 
for  admitting  the  mixture  to  the  cylinder  and  for  expelling  the 
burnt  gases  to  the  atmosphere,  a  device  for  igniting  the  mixture 
at  the  proper  time,  a  mechanism  for  changing  the  reciprocating 
motion  of  the  piston  into  rotary  motion,  a  governor  to  keep  the 
speed  constant  at  variable  loads,  a  lubrication  system  for  the 
cylinder  and  bearings,  an  arrangement  for  cooling  the  cylinder 
walls,  a  flywheel  to  carry  the  engine  through  the  idle  strokes, 
and  bearings  and  a  frame  to  support  the  various  parts. 

Details  concerning  various  types  of  gas  power  plants  will  be 
given  in  Chapter  XI. 

Problems 

1.  Make  a  thorough  study  of  some  non-condensing  steam  power  plant  in 
your  vicinity  and  hand  in  a  report  concerning  the  important  details.  State 
in  which  respects  the  power  plant  you  have  examined  differs  from  that  illus- 
trated in  Fig.  1. 

2.  Make  a  sketch  showing  how  the  piping  in  a  non-condensing  power 
plant  would  be  modified  if  the  exhaust  steam  is  used  for  heating. 

3.  Make  a  study  of  some  internal  combustion  engine  power  plant  and 
hand  in  a  report  concerning  fuel  used  and  fundamental  details  of  the  engine. 


CHAPTER  II 
STEAM  POWER  FUELS  AND  COMBUSTION 

Fuels 

The  fuel  in  the  case  of  the  steam  power  plant  is  burned  under 
the  boiler,  and  its  heat  is  utilized  in  changing  water  into  steam. 

Fuels  may  be  used  in  their  natural  state,  or  may  be  prepared 
or  manufactured  in  various  ways.  The  chief  natural  fuels  are 
coal,  wood,  petroleum  oil,  and  natural  gas.  The  chief  prepared 
fuels  are  coke  made  from  the  distillation  of  coal,  artificial  gas 
made  from  solid  or  liquid  fuels,  and  the  various  petroleum  distil- 
lates. Another  prepared  fuel  is  briqueted  coal  which  is  made  by 
pressing  finely  ground  coal  into  brick  form,  the  particles  being 
held  together  by  some  cementing  material.  There  are  a  great 
many  other  materials  which  could  be  used  for  fuel,  such  as  acety- 
lene, alcohol,  and  benzol,  that  have  valuable  fuel  properties,  but 
their  high  cost  makes  their  use  prohibitive.  Then  again  there  is 
another  class  of  fuel  which  is  derived  as  a  by-product  in  various 
industries.  To  this  class  belongs  gas  discharged  from  blast 
furnaces  which  has  considerable  value  as  a  fuel. 

The  Heating  Value  of  Fuels. — By  the  heating  value  of  a  fuel, 
often  expressed  by  the  terms,  heat  of  combustion,  calorific  value, 
and  heat  content,  is  meant  the  amount  of  heat  liberated  by  the 
perfect  combustion  of  one  unit  weight  of  a  solid  or  liquid  fuel, 
or  of  a  unit  volume  of  a  gaseous  fuel.  The  value  of  the  fuel  for 
power  purposes  is  dependent  upon  its  heat  content  in  a  unit 
weight.  Thus  of  two  grades  of  coal,  the  one  containing  the 
greater  heating  value  is  the  most  desirable  commercially,  other 
things  being  equal. 

The  heating  value  of  the  fuel  is  measured  in  heat  units.  A 
heat  unit  is  the  amount  of  heat  required  to  raise  the  temperature 
of  one  pound  of  water  one  degree.     The  unit  used  in  English 

10 


STEAM  POWER  FUELS  AND  COMBUSTION        11 

speaking  countries  is  the  British  thermal  unit  (B.t.u).  TheB.t.u. 
is  denned  as  the  amount  of  heat  required  to  raise  the  temperature 
of  one  pound  of  water  from  62  to  63  degrees  Fahrenheit.  An- 
other definition  of  a  B.t.u.  is  Jf80  of  the  heat  required  to  raise 
the  temperature  of  one  pound  of  water  from  the  freezing  point 
to  the  boiling  point  on  the  Fahrenheit  scale. 

This  calorific  value  or  the  heating  value  of  a  fuel  may  be 
determined  by  means  of  a  chemical  analysis,  but  a  more  satisfac- 
tory determination  can  be  made  by  an  instrument,  called  a  coal 
calorimeter. 

Several  different  types  of  coal  calorimeters  are  available,  but 
those  of  the  bomb  type,  similar  to  the  one  illustrated  in  Fig.  4, 
are  the  most  accurate  and  satisfactory  for  determining   the 


Fig.  4. — Bomb  calorimeter. 


heating  value  of  solid  and  heavy  liquid  fuels.  This  type  of 
instrument  consists  of  a  steel  vessel  or  bomb,  lined  with  porcelain, 
platinum,  or  gold  to  prevent  corrosion,  and  into  which  a  weighed 
sample  of  the  fuel  is  introduced.  The  bomb,  after  it  has  been 
charged  with  fuel,  is  filled  with  oxygen  from  the  cylinder  0, 
to  which  the  bomb  is  connected  through  the  union  U.  The 
quantity  of  oxygen  admitted  to  the  bomb  is  regulated  by  means 
of  the  valve  W  and  the  pressure  gage  M .  The  bomb  is  then 
placed  in  the  calorimeter  vessel  A ,  which  contains  a  known  weight 


12         STEAM  AND  GAS  POWER  ENGINEERING 

of  water.  The  water  is  agitated  by  the  stirring  mechanism 
shown  and  the  thermometer  T  indicates  its  rise  in  temperature 
when  the  fuel  within  the  bomb  is  burned.  The  calorimeter 
vessel  A  is  fitted  with  a  water  jacket  which  reduces  the  effect 
of  external  changes  of  temperature  and  causes  a  more  uniform 
temperature  of  the  thermometer  T.  The  fuel  charge  is  ignited 
electrically  and  burns  in  the  presence  of  oxygen.  The  heating 
value  of  the  fuel  is  calculated  from  the  observed  temperature  rise 
of  the  water  as  indicated  by  thermometer  T,  since  the  heat 
gained  by  the  water  must  equal  the  heat  given  up  by  the  fuel, 
after  making  allowances  for  radiation  and  other  similar  factors 
which  may  produce  a  gain  or  loss  of  heat. 

The  Proximate  Analysis  of  Fuels. — While  the  heating  value  of 
a  fuel  is  important  in  estimating  its  commercial  value,  other 
properties  must  be  considered  as  well.  Two  different  coals,  for 
instance,  may  have  the  same  heating  value  but  the  properties 
of  one,  not  disclosed  by  the  heating  value,  may  cause  it  to  be 
more  or  less  desirable  than  the  other  coal.  The  proximate 
analysis  of  a  fuel  has  been  devised  to  assist  in  this.  The 
proximate  analysis  determines  the  amount  of  moisture,  volatile 
matter,  fixed  carbon,  ash  and  sulphur. 

Moisture  requires  heat  for  its  evaporation,  and  is  direct  loss. 
Ash,  when  present  in  large  amounts,  will  form  clinkers,  and  is 
also  an  item  of  expense  in  its  disposal.  Sulphur  is  usually  con- 
sidered a  detrimental  constituent,  especially  if  in  amounts  greater 
than  2  per  cent.  Coals  containing  large  quantities  of  sulphur 
are  usually  avoided. 

The  volatile  matter  and  the  fixed  carbon  are  the  heat  producing 
constituents  of  the  coal.  The  volatile  matter  represents  that 
part  which  distils  off  at  a  comparatively  low  temperature,  and 
may  be  considered  the  gaseous  or  flaming  constituent.  The 
amount  of  volatile  matter  gives  some  conception  of  the  smoke 
producing  qualities  of  the  fuel.  If  smokeless  combustion  must 
be  secured  in  any  particular  plant,  and  no  special  furnaces  have 
been  installed  which  will  insure  the  proper  combustion  of  volatile 
gases,  a  coal  with  a  large  content  of  volatile  matter  should  not 
be  selected.  The  fixed  carbon  is  just  the  reverse  of  the  volatile 
matter;  it  being  that  part  of  the  coal  which  burns  without  flame 
and  consequently  gives  no  trouble  from  smoke. 


STEAM  POWER  FUELS  AND  COMBUSTION        13 

Fuels  for  Steam  Generation. — The  fuels  most  commonly  used 
for  steam  generation  are  coal,  wood,  petroleum  oils,  and  natural 
gas. 

Wood  is  but  little  used  for  steam  generation  except  in  remote 
places,  where  timber  is  plentiful,  or  in  special  cases  where  saw- 
dust, shavings,  and  pieces  of  wood  are  by-products  of  manufac- 
turing operations.  Wood  burns  rapidly  and  with  a  bright  flame, 
but  does  not  evolve  much  heat.  When  first  cut,  wood  contains 
30  to  50  per  cent,  of  moisture,  which  can  be  reduced  by  drying 
to  about  15  per  cent.  One  pound  of  dry  wood  is  equal  in  heat- 
producing  value  to  about  %  lb.  of  soft  coal.  It  is  important 
that  wood  be  dry,  as  each  10  per  cent,  of  moisture  reduces  its 
heat-producing  value  as  a  fuel  by  about  12  per  cent.  The  chem- 
ical compositions  and  the  calorific  values  of  some  of  the  more 
common  woods  are  shown  in  Table  1. 

Table  1. — Analysis  and  Calorific  Value  of  Dry  Wood 


Kind  of  wood 

Carbon 

Hydrogen 

Nitrogen 

Oxygen 

Ash 

B.t.u. 
per  pound 

Oak 

50.16 
49.18 
48.99 
49.06 
48.88 
50.36 
50.31 

6.02 
6.27 
6.20 
6.11 
6  06 
5.92 
6.20 

0.09 
0.07 
0.06 
0.09 
0.10 
0.05 
0.04 

43.36 
43.91 
44.25 
44.17 
44.67 
43.39 
43.08 

0.37 
0.57 
0.50 
0.57 
0.29 
0.28 
0.37 

8,316 
8,480 
8,510 

Ash 

Elm 

Beech 

8,591 
8,586 
9,063 
9,153 

Birch 

Fir 

Pine 

Coal  is  more  extensively  used  as  a  fuel  for  steam  generation 
than  any  other  substance.  It  is  a  substance  which  results  from 
collections  of  vegetable  matter,  which  has  been  gradually  changed 
in  physical  and  chemical  composition  until  it  finally  became  coal. 

In  the  first  stages  of  the  transformation  the  material  is  classed 
as  peat.  In  its  next  stage  it  is  known  as  lignite  or  brown  coal. 
Following  this  in  the  proper  order  of  transformation  are  soft  or 
bituminous  coal,  semi-bituminous,  semi-anthracite,  and  finally 
anthracite  or  hard  coal. 

Table  2  gives  the  proximate  analyses  and  the  calorific  values 
of  American  coals. 


14 


STEAM  AND  GAS  POWER  ENGINEERING 


Table  2. — Composition  and  Calorific  Value  of  American  Coals 
(U.  S.  Bureau  of  Mines) 


State 


Classification 


Proximate  analysis 


Mois- 
ture 


Vola- 
tile 
matter 


Fixed 
carbon 


Ash 


Sul- 
phur 


B.t.u. 
per  lb., 
dry  coal 


Pennsylvania.. 
Pennsylvania.. 
Pennsylvania.. 
Pennsylvania.. 
West  Virginia. 

Colorado 

Illinois 

Kansas 

Kentucky 

Missouri 

Ohio 

Oklahoma.  .  .  . 
Pennsylvania.. 
West  Virginia. 

Colorado 

North  Dakota 
Wyoming 


Anthracite 

Anthracite 

Semi-anthracite. 
Semi-bituminous 
Semi-bituminous 

Bituminous 

Bituminous 

Bituminous 

Bituminous 

Bituminous 

Bituminous 

Bituminous 

Bituminous 

Bituminous 

Lignites 

Lignites 

Lignites 


2.19 

3.43 

5.48 

2.72 

3.17 

10.27 

7.12 

11.10 

4.83 

5.87 

5.15 

4.83 

3.48 

3.36 

20.71 

32.65 

23.46 


5.67 
6.79 
7.53 
16.70 
18.46 
38.25 
34.55 
35.51 
33.71 
30.98 
37.34 
35.76 
35.15 
22.50 
31.82 
30.57 
35.64 


86.24 
78.25 
81.00 
75.38 
70.86 
44.99 
50.68 
40.69 
57.73 
51.67 
49.00 
55.55 
55.45 
68.86 
43.98 
28.49 
35.73 


5.90 

11.53 

11.47 

5.20 

7.51 

6.49 

7.65 

12.70 

3.73 

11.48 

8.51 

3.86 

5.92 

5.28 

3.45 

8.29 

5.17 


0.57 
0.46 

0.55 
1.07 
0.42 
2.23 
3.99 
0.82 
5.00 
2.94 
1.34 
1.18 
0.52 
0.45 
1.33 
0.49 


13,828 
12,782 
13,547 
14,521 
13,995 
11,416 
12,481 
11,065 
13,842 
12,339 
12,733 
13,829 
13,700 
14,369 
9,941 
7,357 
9,050 


The  weight  of  coal  per  cubic  foot  will  vary  from  43  to  58 
pounds.  An  anthracite  coal  will  have  a  greater  weight  than  a 
bituminous  coal;  the  higher  the  amount  of  fixed  carbon  in  the 
coal,  the  greater  is  its  weight. 

Anthracite,  commonly  known  as  hard  coal,  is  the  highest  grade 
of  coal.  It  consists  mainly  of  fixed  carbon  having  little,  and  in 
some  cases  no,  volatile  matter.  Some  varieties  approach  graph- 
ite in  their  characteristics,  and  are  burned  with  difficulty  unless 
mixed  with  other  coals.  This  coal  is  slow  to  ignite,  burns  with  a 
short  flame,  and  gives  an  intense  fire  free  from  smoke.  As  it  is 
available  for  steaming  purposes  only  in  certain  limited  sections, 
its  use  is  not  common. 

Semi-anthracite  coal  is  softer  and  lighter  than  anthracite.  It 
contains  less  carbon  than  anthracite  coal,  and  its  volatile  matter 
ranges  from  7  to  12  per  cent.  It  ignites  more  readily  than 
anthracite  and  makes  an  intense,  free-burning  fire. 

Semi-bituminous  coal  has  all  the  physical  characteristics  of 
bituminous  coal,  but  it  differs  from  it  in  that  the  volatile  matter 
content  is  not  so  high.     Semi-bituminous  coal  contains  from  12 


STEAM  POWER  FUELS  AND  COMBUSTION        15 

to  25  per  cent,  volatile  matter,  and  when  compared  with  semi- 
anthracite  coal  its  fixed  carbon  is  less. 

Bituminous  coal  is  a  classification  intended  to  include  coals 
which  contain  20  per  cent,  or  more  volatile  matter  and  less  than 
60  per  cent,  of  fixed  carbon.  One  objection  to  the  use  of  bitu- 
minous coal  as  a  fuel  is  its  smoking  quality.  This  may  be  an 
undesirable  feature,  especially  if  its  use  is  in  a  city  where  smoke 
ordinances  are  enforced  and  when  special  smokeless  furnaces 
have  not  been  installed.  Another  feature  which  may  be  con- 
sidered undesirable  is  the  tendency  for  highly  volatile  coals  to 
ignite  spontaneously. 

Bituminous  coal  constitutes  over  85  per  cent,  of  the  fuel  used 
in  manufacturing,  when  including  the  manufacture  of  coke. 
The  term  bituminous  coal  is  broad  in  its  interpretation,  and 
includes  a  great  variety  of  coals  which  have  many  different  quali- 
ties. For  this  reason  many  of  the  coals  of  this  classification  are 
given  special  names  depending  upon  some  marked  physical 
characteristic  they  possess.  Dry  or  free  burning  bituminous 
coal  is  one  of  the  best  of  the  bituminous  varieties  for  steaming 
purposes.  As  compared  with  other  bituminous  coals,  it  is  low  in 
volatile  matter  and  burns  with  a  short  bluish  flame.  Bituminous 
caking  coals  is  the  term  applied  to  those  varieties  that  swell  up, 
become  pasty  and  fuse  together  in  burning.  They  contain  a 
greater  amount  of  volatile  matter  than  the  dry  bituminous  coals 
and  for  that  reason  burn  with  a  larger  flame  and  have  a  greater 
tendency  to  smoke.  Long  flaming  bituminous  coals  are  those 
containing  the  greatest  amounts  of  volatile  matter.  They  possess 
a  strong  tendency  to  produce  smoke.  Cannel  coal  is  a  variety 
rich  in  volatile  matter.  It  is  used  principally  in  the  manufac- 
ture of  artificial  gas.  It  differs  in  appearance  from  the  other 
varieties  in  that  it  has  a  dull  resinous  luster.  Its  volatile  content 
varies  from  45  to  60  per  cent.  It  is  seldom  used  as  a  steaming 
coal,  though  it  is  sometimes  mixed  with  other  coals  containing 
less  volatile  matter. 

Lignite  may  be  classified  as  coal  in  the  process  of  formation. 
This  coal  contains  a  very  large  proportion  of  volatile  matter 
and  less  than  50  per  cent,  fixed  carbon.  However,  it  has  a  good 
heating  value  and  burns  freely,  but  owing  to  the  high  percentage 
of  volatile  matter  it  will  not  stand  storage,  but  crumbles  badly 


16 


STEAM  AND  GAS  POWER  ENGINEERING 


soon  after  exposure  to  air.  Its  use  is  restricted  to  those  localities 
in  which  it  is  found. 

Other  solid  fuels  used  to  some  extent  for  steam  generation  are : 
Peat,  which  is  an  intermediate  between  wood  and  coal  and  is 
found  in  bogs;  sawdust;  oak  bark  after  it  has  been  used  in  the 
process  of  tanning;  bagasse,  or  the  refuse  of  cane  sugar;  and 
cotton  stalks.  Coke  is  also  used  to  some  extent,  the  advantage  of 
this  fuel  as  compared  with  coal  being  that  coke  will  not  ignite 
spontaneously,  will  not  deteriorate  or  decompose  when  exposed 
to  the  atmosphere,  and  produces  no  smoke  when  burned.  Coke 
is  manufactured  by  burning  coal  in  a  limited  air  supply,  the 
volatile  hydrocarbons  being  driven  off  during  the  process. 

Petroleum  fuels,  either  in  the  form  of  crude  petroleum  or  as  the 
refuse  left  from  its  distillation,  are  used  for  making  steam  to  a 
considerable  extent  in  certain  parts  where  the  relative  cost 
of  oil  is  less  than  that  of  coal.  It  has  been  estimated  that 
petroleum  oils  at  2  c.  per  gallon  are  equally  economical  for  steam 
making  with  coal  at  $3  per  ton.  The  advantages  of  oil,  as  com- 
pared with  solid  fuels,  are  ease  of  handling,  cleanliness,  and 
absence  of  smoke  after  combustion.  Table  3  gives  the  analysis 
and  heating  value  of  several  American  petroleum  oils. 

Table  3. — Analysis  and  Calorific  Value  of  Oils  (C.  E.  Lucke) 


Classification 

Density   at 
60°F. 

Ultimate  analysis 

Heating  value 
B.t.u.  per  lb. 

gr- 

°B6. 

C 

H2 

o2+ 

N2 

s 

High 

Low 

California  fuel 

0.966 
0.926 
0.957 
0.924 
0.914 
0.866 
0.841 
0.829 

14.93 
21.25 
16.24 
21.56 
23.18 
31.67 
36.47 
38.89 

81.52 
83.26 
86.30 
84.60 
86.10 
85.40 
84.30 
85.00 

11.61 
12.41 
16.70 
10.90 
13.90 
13.07 
14.10 
13.80 

6.92 
3.83 

2.97 

1.6 
0.6 

0.55 
0.50 
0.80 
1.63 
0.06 

0.6 

18,926 
19,654 
21,723 
18,977 
20,949 
20,345 
20,809 
20,752 

17,903 

Texas,  Beaumont  fuel 

California  crude 

18,570 
21,254 

Texas,  Beaumont  crude 

Pennsylvania  crude 

18,025 
19,735 

19,203 

West  Virginia  crude 

Ohio  crude 

19,578 
19,547 

Natural  gas  is  used  for  steam  generation  only  in  natural  gas 
regions,  where  its  cost  is  very  low.  If  the  cost  of  natural  gas  is 
greater  than  10  cents  per  1,000  cu.  ft.,  it  cannot  compete  with 
coal  at  $3  a  ton.  Illuminating  gas  and  other  artificial  gas  is 
too  expensive  for  steam  generation  and  cannot  compete  with 


STEAM  POWER  FUELS  AND  COMBUSTION        17 

other  fuels.     The  heating  values  of  various  gaseous  fuels  will  be 
found  in  Table  4. 

Table  4. — Heating  Value  of  Gaseous  Fuels 

Character  of  Gas  B.t.u.  per  cu.  ft. 

Coke-oven  Gas 600 

Water  Gas 275 

Blast  Furnace  Gas 100 

Natural  Gas 950 

Producer  Gas 120 

Fuels  suitable  for  internal  combustion  engines  are  treated  in 
Chapter  XII. 

Combustion. — Combustion  is  a  chemical  combination  of  the 
heat-producing  constituents  of  a  fuel  with  oxygen,  accompanied 
by  the  evolution  of  heat. 

Carbon,  hydrogen,  and  sulphur  are  the  main  combustible  con- 
stituents of  all  fuels.  Of  these,  the  sulphur  is  of  minor  impor- 
tance in  contributing  to  the  heating  value,  because  it  is  present 
in  small  quantities  in  fuels  suitable  for  steam  power  plants. 
Carbon  is  present  either  in  a  free,  uncombined  state  or  in  com- 
bination with  hydrogen  as  a  hydrocarbon. 

Oxygen,  the  supporter  of  combustion,  is  one  of  the  most  com- 
mon substances  found  in  nature.  The  largest  supply  of  oxygen 
is  found  in  the  atmosphere,  and  it  is  from  this  source  that  the 
supply  required  for  the  combustion  of  fuel  is  derived.  Air  is 
chiefly  a  mixture  of  oxygen  and  nitrogen,  although  small  amounts 
of  other  gases  are  usually  present. 

Air  contains  0.23  parts  by  weight  of  oxygen  and  0.77  parts  by 
weight  of  nitrogen.  Only  the  oxygen  is  used  in  the  combustion 
of  the  fuel;  nitrogen  is  an  inert  gas  and  has  no  chemical  effect  upon 
the  combustion  of  the  fuel. 

Chemistry  of  Combustion. — In  the  process  of  combustion,  the 
heat  producing  elements  of  the  fuel,  which  are  carbon,  hydrogen, 
and  sulphur,  unite  with  oxygen  from  the  air. 

If  the  combustion  is  perfect,  the  combustibles  unite  with  the 
greatest  amount  of  oxygen.  Thus  in  the  case  of  carbon,  if  the 
combustion  is  perfect,  every  atom  of  carbon  unites  with  two 
atoms  of  oxygen  forming  carbon  dioxide  (C  +  02  =  C02),  and 
liberates  14,600  B.t.u.  per  pound. 


18         STEAM  AND  GAS  POWER  ENGINEERING 

If  there  is  a  lack  of  oxygen,  combustion  is  imperfect,  every 
atom  of  carbon  unites  only  with  one  atom  of  oxygen  forming 
carbon  monoxide  (C  +  O  =  CO)  and  liberating  only  4,400  B.t.u. 
for  each  pound  of  carbon  burned. 

Hydrogen,  when  burned,  enters  into  combination  with  oxygen, 
as  indicated  by  the  following  chemical  reaction,  forming  water 
(H20): 

H2  +  0  =  H20 

The  sulphur  unites  with  oxygen  to  form  sulphur  dioxide,  as 
indicated  by  the  following  reaction: 

S  +  02  =  S02 

The  importance  of  proper  air  supply  in  the  burning  of  a  fuel 
is  quite  evident  from  the  above.  Each  pound  of  carbon  when 
completely  burned  is  capable  of  liberating  14,600  B.t.u.  If  car- 
bon is  burned  to  carbon  monoxide,  only  4,400  B.t.u.  will  be  liber- 
ated, producing  a  loss  of  10,200  B.t.u.,  which  is  about  70  per  cent, 
of  the  original  heating  value  of  the  carbon.  While  it  would  be 
an  extremely  inefficient  furnace  that  would  produce  much  carbon 
monoxide,  any  furnace,  unless  properly  operated,  produces  more 
or  less  incomplete  combustion,  with  the  consequent  lower  effi- 
ciency in  the  utilization  of  the  fuel. 

Air  Required  for  Combustion. — For  the  complete  combustion 
of  one  pound  of  carbon  2.66  pounds  of  oxygen,  or  11.5  pounds  of 
air  will  be  theoretically  required.  Complete  combustion  will  not 
be  obtained  in  a  boiler  furnace  if  only  this  theoretical  amount  of 
air  is  supplied.  An  excess  of  air  varying  from  50  to  100  per 
cent,  will  be  required,  depending  upon  the  draft  and  upon  the 
fuel  used.  With  natural  draft,  a  greater  excess  of  air  is 
required  than  with  mechanical  draft. 

Too  much  air  will  produce  a  great  loss  of  heat  by  diluting  the 
gases  arising  from  the  furnace.  Air  should  be  added  to  the 
furnace  so  that  each  atom  of  carbon  has  sufficient  opportunity  to 
unite  with  as  much  air  as  possible.  When  this  is  accomplished  no 
further  excess  air  is  needed.  Ordinarily,  bituminous  coal  re- 
quires about  20  pounds  of  air  per  pound  of  fuel,  or  about  250 
cubic  feet  of  air  per  pound  of  fuel. 

Flue  Gas  Analysis. — The  analysis  of  the  gases  leaving  the 
boiler  is  made  to  ascertain  whether  the  fuel  is  being  burned 


STEAM  POWER  FUELS  AND  COMBUSTION       19 

economically.  If  there  is  an  excess  of  air,  too  much  oxygen  will 
be  present  in  the  flue  gases;  if  there  is  a  deficiency  there  will  be 
carbon  monoxide  present. 

Many  instruments  have  been  devised  to  facilitate  this  analysis. 
The  fundamental  principles  upon  which  they  operate  are  much 
the  same.     A  simple  device,  called  an  Orsat  apparatus  and  shown 


From  Flue 


Fia.  5. — Orsat  apparatus. 


in  Fig.  5,  is  commonly  used.  It  consists  of  three  pipettes,  A, 
B,  and  C,  filled  respectively  with  caustic  potash,  a  mixture  cf 
caustic  potash  and  pyrogallic  acid,  and  cuprous  chloride.  A 
measuring  burette,  M,  and  a  displacement  bottle,  W,  is  also 
provided.  The  sample  of  the  flue  gas  to  be  analyzed  is  drawn 
into  the  measuring  burette.  It  is  then  passed  into  the  pipette 
A   containing  the  caustic  potash  where  the  carbon  dioxide  is 


20         STEAM  AND  GAS  POWER  ENGINEERING 

absorbed.  The  gas  is  then  drawn  back  into  the  measuring 
burette  and  the  shrinkage  in  volume  represents  the  amount  of 
carbon  dioxide  present.  The  remaining  gas  is  similarly  treated 
in  pipette  B  where  the  oxygen  is  absorbed,  and  is  finally  passed  to 
pipette  C  where  the  carbon  monoxide  is  removed. 

Perfect  combustion  is  indicated  by  a  flue  gas  analysis,  which 
shows  about  1  per  cent,  of  carbon  dioxide  for  every  4  per  cent, 
of  nitrogen.  Low  carbon  dioxide  may  be  due  to  excessive  air, 
air  holes  in  the  fuel  bed,  or  to  the  infiltration  of  air  through  cracks 
in  the  setting.  Dirty  heating  surfaces  and  the  presence  of  soot 
will  be  indicated  by  a  low  carbon  dioxide  in  the  flue  gases.  Too 
much  oxygen  in  the  flue  gases  shows  excess  of  air.  A  good  flue 
gas  analysis  will  show  4  to  8  per  cent,  oxygen,  10  to  13  per  cent, 
carbon  dioxide,  and  no  carbon  monoxide. 

Problems 

1.  Coal  costs  $3.00  a  ton  (2,000  lbs.).  If  the  coal  in  question  has  a  heat- 
ing value  of  12,000  B.t.u.  per  lb  ,  what  is  the  cost  in  cents  of  1,000  B.t.u.? 

2.  Natural  gas  costs  15  c.  per  1,000  cubic  feet.  If  its  heating  value  is  950 
B.t.u.  per  cu.  ft.,  what  is  the  cost  of  1,000  B.t.u.? 

3.  Fuel  oil  whose  heating  value  is  18,500  B.t.u.  per  pound  sells  at  5  c. 
per  gallon.  Coal  with  a  heating  value  of  13,000  B.t.u.  per  pound  may  be 
purchased  at  a  price  of  $4.00  per  ton.  Which  would  be  the  cheaper  fuel  if 
the  estimate  is  based  upon  the  cost  of  an  equal  number  of  heat  units? 

4.  Compile  a  table  showing  composition  and  heating  value  of  the  fuels 
most  commonly  used  in  your  locality. 

5.  Prove  that  2%  pounds  of  oxygen  will  be  required  to  burn  1  pound 
of  carbon  into  carbon  dioxide. 

6.  Prove  that  11^  pounds  of  air  will  be  required  to  supply  2%  pounds 
of  oxygen. 


CHAPTER  III 
STEAM 

Theory  of  Steam  Generation. — If  heat  is  added  to  ice,  the 
effect  will  be  to  raise  its  temperature  until  the  thermometer  regis- 
ters 32°F.  When  this  point  is  reached  a  further  addition  of 
heat  does  not  produce  an  increase  in  temperature  until  all  the  ice 
is  changed  into  water,  or  in  other  words,  the  ice  melts.  It  has 
been  found  experimentally  that  144  B.t.u.  are  required  to  change 
1  pound  of  ice  into  water.  This  quantity  is  called  the  latent 
heat  of  liquefaction  of  ice. 

After  the  given  quantity  of  ice,  which  for  simplicity  may  be 
taken  as  1  pound,  has  all  been  turned  into  water,  it  will  be  found 
that  if  more  heat  is  added  the  temperature  of  the  water  will  again 
increase,  though  not  as  rapidly  as  did  that  of  the  ice.  While  the 
addition  of  each  British  thermal  unit  increases  the  temperature 
of  ice  2°F.,  in  the  case  of  water  an  increase  of  only  about  1°  will 
be  noticed  for  each  British  thermal  unit  of  heat  added.  This 
difference  is  due  to  the  fact  that  the  specific  heat,  or  the  resistance 
offered  by  ice  to  a  change  in  temperature  is  only  one-half  that 
offered  by  water.     That  is,  the  specific  heat  of  ice  is  0.5. 

If  the  water  is  heated  in  a  vessel  open  to  the  atmosphere,  its 
temperature  will  continue  to  rise  until  it  reaches  a  temperature  of 
about  212°F.,  the  boiling  point  of  water,  when  further  addition  of 
heat  will  not  produce  any  temperature  changes,  but  steam  will 
issue  from  the  vessel.  It  has  been  found  that  about  970  B.t.u. 
are  required  to  change  1  pound  of  water  at  atmospheric  pressure 
and  at  212°F.  into  steam.  The  quantity  of  heat  so  supplied 
which  changes  the  physical  state  of  water  from  the  liquid  state  to 
steam  is  called  the  latent  heat  of  vaporization. 

If  the  above  operations  are  performed  in  a  closed  vessel, 
such  as  an  ordinary  steam  boiler,  water  will  boil  at  a  higher  tem- 
perature than  212°F.,  since  the  steam  driven  off  cannot  escape 

21 


22         STEAM  AND  GAS  POWER  ENGINEERING 

and  is  compressed,  raising  the  pressure  and  consequently  the 
temperature. 

The  fact  that  the  boiling  point  of  water  depends  on  the  pressure 
is  well  known.  Thus  in  a  locality  where  the  altitude  is  6,000  ft. 
above  sea  level  and  the  barometric  pressure  is  12.6  pounds  per 
square  inch  the  boiling  point  of  water  is  about  204°F.  as  compared 
with  212°F.  at  sea  level  where  the  barometric  pressure  is  14.7 
pounds  per  square  inch. 

Assuming  that  the  pressure  is  increased  to  60  pounds  per 
square  inch  by  the  gage,  it  will  be  found  that  the  boiling  point  of 
water  is  307.3°F.  At  100  pounds  per  square  inch  water  will 
boil  at  337. 9°F.  and  at  150  pounds  the  temperature  will  read 
365.9°F.  before  steam  will  be  formed. 

Quality  of  Steam. — Steam  formed  in  contact  with  water  is 
known  as  saturated  steam,  which  may  be  wet  or  dry. 

In  the  first  case  steam  carries  with  it  a  certain  amount  of  water 
which  has  not  been  evaporated.  The  percentage  of  this  water 
determines  the  condition  or  the  quality  of  the  steam;  that  is,  if 
the  steam  contains  3  per  cent,  by  weight  of  moisture,  the  steam 
is  spoken  of  as  being  97  per  cent.  dry.  A  stationary  steam 
boiler,  properly  erected  and  operated  and  of  suitable  size,  should 
generate  steam  that  is  98  per  cent.  dry.  If  there  is  more  than  3 
per  cent,  moisture,  there  is  every  reason  to  believe  that  the  boiler 
is  improperly  installed,  inefficiently  operated,  has  too  small  a 
space  for  the  disengagement  of  the  steam  from  the  water,  or  is 
too  small  for  the  work  to  be  done. 

In  the  second  condition,  that  of  being  dry  steam,  the  vapor 
carries  with  it  no  water  that  has  not  been  evaporated ;  that  is,  it 
is  dry.  Any  loss  of  heat,  however  small,  not  accompanied  by  a 
corresponding  reduction  in  pressure,  will  cause  condensation, 
and  wet  steam  will  be  the  result.  Steam,  whether  wet  or  dry, 
has  a  definite  temperature  corresponding  to  its  pressure. 

An  increase  in  temperature  not  accompanied  by  an  increase  in 
pressure  will  cause  the  steam  to  acquire  a  condition  that  will 
permit  a  loss  of  heat  at  constant  pressure  without  condensation 
necessarily  following.  This  condition  is  called  superheat. 
The  advantage  of  superheated  steam  lies  in  the  fact  that  its  tem- 
perature may  be  reduced  by  the  amount  of  superheat  without 
causing  condensation.     This  makes  it  possible  to  transmit  the 


STEAM 


23 


steam  through  mains  and  still  have  it  dry  and  saturated  at  the 
time  it  reaches  the  engine  cylinder.  Superheated  steam  may  be 
secured  by  passing  saturated  steam  through  coils  of  pipe  'in  the 
path  of  the  hot  flue  gases  from  the  boiler  to  the  chimney.  An 
apparatus  for  superheating  steam  is  called  a  superheater. 

The  pressure  of  steam  will  remain  constant  if  it  is  used  as  fast 
as  it  is  generated.  If  an  engine  uses  steam  too  rapidly  the  boiler 
pressure  will  drop,  and  similarly  if  the  fuel  is  burned  at  a  constant 
rate  and  an  insufficient  amount  of  steam  is  used  the  pressure  of 
the  steam  in  the  boiler  will  increase. 

Steam  Tables. — In  Table  5  are  given  some  of  the  most  impor- 
tant properties  of  saturated  steam,  which  include: 

1.  Pressure  of  steam  in  pounds  per  square  inch  absolute  (p). 
This  column  gives  the  total  pressure  exerted  and  is  the  sum  of  the 
gage  pressure  which  measures  the  pressures  above  that  of  the 
atmosphere  and  the  atmospheric  pressure  as  indicated  by  the 
barometer.  A  barometric  reading  of  30  inches  corresponds  to  a 
pressure  of  14.7  pounds  per  square  inch. 


Table  5. — Properties  of  Saturated  Steam 

(Marks  and  Davis) 
ENGLISH   UNITS 


m  O 
5°* 

gs 

w 

gg 

h 

43 

is 

turn 

Specific 

Volume 

Cu.  Ft.  per 

Pound 

M 

Ill 

Si* 

V 

t 

h 

L 

H 

V 

I 

V 

V 

.0886 

32 

0 

1072.6 

1072.6 

3301.0 

.000303 

.0886 

.2562 

60 

28.1 

1057.4 

1085.5 

1207.5 

.000828 

.2562 

.5056 

80 

48.1 

1046.6 

1094.7 

635.4 

.001573 

.5056 

1 

101.8 

69.8 

1034.6 

1104.4 

333.00 

.00300 

1 

2 

126.1 

94.1 

1021.4 

1115.5 

173.30 

.00577 

2 

3 

141.5 

109.5 

1012.3 

1121.8 

118.50 

.00845 

3 

4 

153.0 

120.9 

1005.6 

1126.5 

90.50 

.01106 

4 

5 

162.3 

130.2 

1000.2 

1130.4 

73.33 

.01364 

5 

6 

170.1 

138.0 

995.7 

1133.7 

61.89 

.01616 

6 

7 

176.8 

144.8 

991,7 

1136.5 

53.58 

.01867 

7 

8 

182.9 

150.8 

988.1 

1138.9 

47.27 

.02115 

8 

24 


STEAM  AND  GAS  POWER  ENGINEERING 


Properties  of  Saturated  Steam  —  Continued 

ENGLISH  UNITS 


it 

< 

8  • 

&£ 

8  1 

■ 

4*3 

§a 

n 

n 

-£  c3  O 
(JO 

la 

Specific 

Volume 

Cu.  Ft.  per 

Pound 

tigs 
ftjo 

11* 

(-I'D  . 
PhAcJ 

V 

t  . 

h 

L 

H 

V 

1 

| 

P 

9 

188.3 

156.3 

984.8 

1141.1 

42.36 

.02361 

9 

10 

193.2 

161.2 

981.8 

1143.0 

38.38 

.02606 

10 

11 

197.7 

165.8 

979.0 

1144.8 

35.10 

.02849 

11 

12 

202.0 

170.0 

976.4 

1146.4 

32.38 

.03089 

12 

13 

205.9 

173.9 

974.0 

1147.9 

30.04 

.03329 

13 

14 

209.6 

177.6 

971.7 

1149.3 

28.02 

.03568 

14 

14.7 

212.0 

180.1 

970.4 

1150.4 

26.79 

.03733 

14.7 

15 

213.0 

181.1 

969.5 

1150.6 

26.27 

.03806  • 

15 

16 

216.3 

184.5 

967.4 

1151.9 

24.77 

.04042 

16 

17 

219.4 

187.7 

965.4 

1153.1 

23.38 

.04277 

17 

18 

222.4 

190.6 

963.5 

1154.1 

22.16 

.04512 

18 

19 

225.2 

193.5 

961.6 

1155.1 

21.07 

.04746 

19 

20 

228.0 

196.2 

959.8 

1156.0 

20.08 

.04980 

20 

21 

230.6 

198.9 

958.0 

1156.9 

19.18 

.05213 

21 

22 

233.1 

201.4 

956.4 

1157.8 

18.37 

.05445 

22 

23 

235.5 

203.9 

954.8 

1158.7 

17.62 

.05676 

23 

24 

237.8 

206.2 

953.2 

1159.4 

16.93 

.05907 

24 

25 

240.1 

208.5 

951.7 

1160.2 

16.30 

.0614 

25 

26 

242.2 

210.7 

950.3 

1161.0 

15.71 

.0636 

26 

27 

244.4 

212.8 

948.9 

1161.7 

15.18 

.0659 

27 

28 

246.4 

214.9 

947.5 

1162.4 

14.67 

.0682 

28 

29 

248.4 

217.0 

946.1 

1163.1 

14.19 

.0705 

29 

30 

250.3 

218.9 

944.8 

1163.7 

13.74 

.0728 

30 

31 

252.2 

220.8 

943.5 

1164.3 

13.32 

.0751 

31 

32 

254.1 

222.7 

942.2 

1164.9 

12.93 

.0773 

32 

33 

255.8 

224.5 

941.0 

1165.5 

12.57 

.0795 

33 

34 

257.6 

226.3 

939.8 

1166.1 

12.22 

.0818 

34 

35 

259.3 

228.0 

938.6 

1166.6 

11.89 

.0841 

35 

36 

261.0 

229.7 

937.4 

1167.1 

11.58 

.0863 

36 

37 

262.6 

231.4 

936.3 

1167.7 

11.29 

.0886 

37 

38 

264.2 

233.0 

935.2 

1168.2 

11.01 

.0908 

38 

39 

265.8 

234.6 

934.1 

1168.7 

10.74 

.0931 

39 

40 

267.3 

236.2 

933.0 

1169.2 

10.49 

.0953 

40 

41 

268.7 

237.7 

931.9 

1169.6 

10.25 

.0976 

41 

42 

270.2 

239.2 

930.9 

1170.1 

10.02 

.0998 

42 

43 

271.7 

240.6 

929.9 

1170.5 

9.80 

.1020 

43 

44 

273.1 

242.1 

928.9 

1171.0 

9.59 

.1043 

44 

45  - 

274.5 

243.5 

927.9 

1171.4 

9.39 

.1065 

45 

46 

275.8 

244.9 

926.9 

1171.8 

9.20 

.1087 

46 

STEAM 


25 


Properties  op  Saturated  Steam  —  Continued 

ENGLISH   UNITS 


8* 

1 

Si 

6 

Is 

h)  o 

o  a 

3  J 

Specific 

Volume 

Cu.  Ft.  per 

Pound 

IT- 

< 

V 

i 

h 

L 

H 

V 

i 

V 

V 

47 

277.2 

246.2 

926.0 

1172.2 

9.02 

.1109 

47 

48 

278.5 

247.6 

925.0 

1172.6 

8.84 

.1131 

48 

49 

279.8 

248.9 

924.1 

1173.0 

8.67 

.1153 

49 

50 

281.0 

250.2 

923.2 

1173.4 

8.51 

.1175 

50 

51 

282.3 

251.5 

922.3 

1173.8 

8.35 

.1197 

51 

52 

283.5 

252.8 

921.4 

1174.2 

8.20 

.1219 

52 

53 

284.7 

254.0 

920.5 

1174.5 

8.05 

.1241 

53 

54 

285.9 

255.2 

919.6 

1174.8 

7.91 

.1263 

54 

55 

287.1 

256.4 

918.7 

1175.1 

7.78 

.1285 

55 

56 

288.2 

257.6 

917.9 

1175.5 

7.65 

.1307 

56 

57 

289.4 

258.8 

917.1 

1175.9 

7.52 

.1329 

57 

58 

290.5 

259.9 

916.2 

1176.1 

7.40 

.1351 

58 

59 

291.6 

261.1 

915.4 

1176.5 

7.28 

.1373 

59 

60 

292.7 

262.2 

914.6 

1176.8 

7.17 

.1394 

60 

61 

293.8 

263.3 

913.8 

1177.1 

7.06 

.1416 

61 

62 

294.9 

264.4 

913.0 

1177.4 

6.95 

.1438 

62 

63 

295.9 

265.5 

912.2 

1177.7 

6.85 

.1460 

63 

64 

297.0 

266.5 

911.5 

1178.0 

6.75 

.1482 

64 

65 

298.0 

267.6 

910.7 

1178.3 

6.65 

.1503 

65 

66 

299.0 

268.6 

910.0 

1178.6 

6.56 

.1525 

66 

67 

300.0 

269.7 

909.2 

1178.9 

6.47 

.1547 

67 

68 

301.0 

270.7 

908.4 

1179.1 

6.38 

.1569 

68 

69 

302.0 

271.7 

907.7 

1179.4 

6.29 

.1591 

69 

70 

302.9 

272.7 

906.9 

1179.6 

6.20 

.1612 

70 

71 

303.9 

273.7 

906.2 

1179.9 

6.12 

.1634 

71 

72 

304.8 

274.6 

905.5 

1180.1 

6.04 

.1656 

72 

73 

305.8 

275.6 

904.8 

1180.4 

5.96 

.1678 

73 

74 

306.7 

276.6 

904.1 

1180.7 

5.89 

.1699 

74 

75 

307.6 

277.5 

903.4 

1180.9 

5.81 

.1721 

75 

76 

308.5 

278.5 

902.7 

1181.2 

5.74 

.1743 

76 

77 

309.4 

279.4 

902.1 

1181.5 

5.67 

.1764 

77 

78 

310.3 

280.3 

901.4 

1181.7 

5.60 

.1786 

78 

79 

311.2 

281.2 

900.7 

1181.9 

5.54 

.1808 

79 

80 

312.0 

282.1 

900.1 

1182.2 

5.47 

.1829 

80 

81 

312.9 

283.0 

899.4 

1182.4 

5.41 

.1851 

81 

82 

313.8 

283.8 

898.8 

1182.6 

5.34 

.1873 

82 

83 

314.6 

284.7 

898.1 

1182.8 

5.28 

.1894 

83 

84 

315.4 

285.6 

897.5 

1183.1 

5.22 

.1915 

84 

85 

316.3 

286.4 

896.9 

1183.3 

5.16 

.1937 

85 

26 


STEAM  AND  GAS  POWER  ENGINEERING 


Phoperties  of  Saturated  Steam  —  Continued 


ENGLISH    UNITS 


Hi 

o5  §M 
.2  ft 

2  • 
fft, 

Is 
£  s 
fj 

la 
m 

+>  1 

.2W 
h?  8 

<o  8 

cSCQ 

Specific 

Volume 

Cu.  Ft.  per 

Pound 

u 

§  g  3 

Ah 

02  O  -1 

< 

P 

i 

h 

L 

H 

V 

1 

w 

p 

86 

317.1 

287.3 

896.2 

1183.5 

5.10 

.1959 

86 

87 

317.9 

288.1 

895.6 

1183.7 

5.05 

.1980 

87 

88 

318.7 

288.9 

895.0 

1183.9 

5.00 

.2002 

88 

89 

319.5 

289.8 

894.3 

1184.1 

4.94 

.2024 

89 

90 

320.3 

290.6 

893.7 

1184.3 

4.89 

.2045 

90 

91 

321.1 

291.4 

893.1 

1184.5 

4.84 

.2066 

91 

92 

321.8 

292.2 

892.5 

1184.7 

4.79 

.2088 

92 

93 

322.6 

293.0 

891.9 

1184.9 

4.74 

.2110 

93 

94 

323.4 

293.8 

891.3 

1185.1 

4.69 

.2131 

94 

95 

324.1 

294.5 

890.7 

1185.2 

4.65 

.2152 

95 

96 

324.9 

295.3 

890.1 

1185.4 

4.60 

.2173 

96 

97 

325.6 

296.1 

889.5 

1185.6 

4.56 

.2194 

97 

98 

326.4 

296.8 

889.0 

1185.8 

4.51 

.2215 

98 

99 

327.1 

297.6 

888.4 

1186.0 

4.47 

.2237 

99 

100 

327.8 

298.4 

887.8 

1186.2 

4.430 

.2257 

100 

101 

328.6 

299.1 

887.2 

1186.3 

4.389 

.2278 

101 

102 

329.3 

299.8 

886.7 

1186.5 

4.349 

.2299 

102 

103 

330.0 

300.6 

886.1 

1186.7 

4.309 

.2321 

103 

101 

330.7 

301.3 

885.6 

1186.9 

4.270 

.2342 

104 

105 

331.4 

302.0 

885.0 

1187.0 

4.231 

.2364 

105 

106 

332.0 

302.7 

884.5 

1187.2 

4.193 

.2385 

106 

107 

332.7 

303.4 

883.9 

1187.3 

4.156 

.2407 

107 

108 

333.4 

304.1 

883.4 

1187.5 

4.119 

.2428 

108 

109 

334.1 

304.8 

882.8 

1187.6 

4.082 

.2450 

109 

110 

334.8 

305.5 

882.3 

1187.8 

4.047 

.2472 

110 

111 

335.4 

306.2 

881.8 

1188.0 

4.012 

.2493 

111 

112 

336.1 

306.9 

881.2 

1188.1 

3.977 

.2514 

112 

113 

336.8 

307.6 

880.7 

1188.3 

3.944 

.2535 

113 

114 

337.4 

308.3 

880.2 

1188.5 

3.911 

.2557 

114 

114.7 

337.9 

308.8 

879.8 

1188.6 

3.888 

.2572 

114.7 

115 

338.1 

309.0 

879.7 

1188.7 

3.878 

.2578 

115 

116 

338.7 

309.6 

879.2 

1188.8 

3.846 

.2600 

116 

117 

339.4 

310.3 

878.7 

1189.0 

3.815 

.2621 

117 

118 

340.0 

311.0 

878.2 

1189.2 

3.784 

.2642 

118 

119 

340.6 

311.7 

877.6 

1189.3 

3.754 

.2663 

119 

120 

341.3 

312.3 

877.1 

1189.4 

3.725 

.2684 

120 

121 

341.9 

313.0 

876.6 

1189.6 

3.696 

.2706 

121 

122 

342.5 

313.6 

876.1 

1189.7 

3.667 

.2727 

122 

123 

343.2 

314.3 

875.6 

1189.9 

3.638 

.2749 

123 

STEAM 


27 


Properties  op  Saturated  Steam  —  Continued 

ENGLISH    UNITS 


3  v 

11* 

3Em 

IB 

e 
A 

fill 

P 

►3o 

ml 

Specific 

Volume 

Cu.  Ft.  per 

Pound 

§  O  3 

o5  g^ 

< 

p 

t 

h 

L 

// 

V 

i 

V 

V 

124 

343.8 

314.9 

875.1 

1190.0 

3.610 

.2770 

124: 

125 

344.4 

315.5 

874.6 

1190.1 

3.582 

.2792 

125 

126 

345.0 

316.2 

874.1 

1190.3 

3.555 

.2813 

126 

127 

345.6 

316.8 

873.7 

1190.5 

3.529 

.2834 

127 

128 

346.2 

317.4 

873.2 

1190.6 

3.503 

.2855 

128 

129 

346.8 

318.0 

872.7 

1190.7 

3.477 

.2876 

129 

130 

347.4 

318.6 

872.2 

1190.8 

3.452 

.2897 

130 

131 

348.0 

319.3 

871.7 

1191.0 

3.427 

.2918 

131 

132 

348.5 

319.9 

871.2 

1191.1 

3.402 

.2939 

132 

133 

349.1 

320.5 

870.8 

1191.3 

3.378 

.2960 

133 

134 

349.7 

321.0 

870.4 

1191.4 

3.354 

.2981 

134 

135 

350.3 

321.6 

869.9 

1191.5 

3.331 

.3002 

135 

136 

350.8 

322.2 

869.4 

1191.6 

3.308 

.3023 

136 

137 

351.4 

322.8 

868.9 

1191.7 

3.285 

.3044 

137 

138 

352.0 

323.4 

868.4 

1191.8 

3.263 

.3065 

138 

139 

352.5 

324.0 

868.0 

1192.0 

3.241 

.3086 

139 

140 

353.1 

324.5 

867.6 

1192.1 

3.219 

.3107 

140 

141 

353.6 

325.1 

867.1 

1192.2 

3.198 

.3128 

141 

142 

354.2 

325.7 

866.6 

1192.3 

3.176 

.3149 

142 

143 

354.7 

326.3 

866.2 

1192.5 

3.155 

.3170 

143 

144 

355.3 

326.8 

865.8 

1192.6 

3.134 

.3191 

144 

145 

355.8 

327.4 

865.3 

1192.7 

3.113 

.3212 

145 

146 

356.3 

327.9 

864.9 

1192.8 

3.093 

.3233 

146 

147 

356.9 

328.5 

864.4 

1192.9 

3.073 

.3254 

147 

148 

357.4 

329.0 

864.0 

1193.0 

3.053 

.3275 

148 

149 

357.9 

329.6 

863.5 

1193.1 

3.033 

.3297 

149 

150 

358.5 

330.1 

863.1 

1193.2 

3.013 

.3319 

150 

152 

359.5 

331.2 

862.3 

1193.5 

2.975 

.3361 

152 

154 

360.5 

332.3 

861.4 

1193.7 

2.939 

.3403 

154 

156 

361.6 

333.4 

860.5 

1193.9 

2.903 

.3445 

156 

158 

362.6 

334.4 

859.7 

1194.1 

2.868 

.3487 

158 

160 

363.6 

335.5 

858.8 

1194.3 

2.834 

.3529 

160 

162 

364.6 

336.6 

858.0 

1194.6 

2.801 

.3570 

162 

164 

365.6 

337.6 

857.2 

1194.8 

2.768 

.3613 

164 

166 

366.5 

338.6 

856.4 

1195.0 

2.736 

.3655 

166 

168 

367.5 

339.6 

855.5 

1195.1 

2.705 

.3697 

168 

170 

368.5 

340.6 

854.7 

1195.3 

2.674 

.3739 

170 

172 

369.4 

341.6 

853.9 

1195.5 

2.644 

.3782 

172 

174 

370.4 

342.5 

853.1 

1195.6 

2.615 

.3824 

174 

176 

371.3 

343.5 

852.3 

1195.8 

2.587 

.3865 

176 

28 


STEAM  AND  GAS  POWER  ENGINEERING 


Properties  op  Saturated  Steam 
english  units 


Concluded 


h 

Jr'a  . 
3* 

0)  , 

a  ho 

j 

■*»  3 

CJ.J 

M 

w 

c3  A 
D  5  m 

■B  *.2 
A  o 

<u  a 
n  1 

Specific 

Volume 

Cu.  Ft.  per 

Pound 

Is  3 
Qgo 

&D 

Sa  • 

figj4 

P 

t 

h 

L 

H 

V 

1 

V 

P 

178 

372.2 

344.5 

851.5 

1196.0 

2.560 

.3907 

178 

180 

373.1 

345.4 

850.8 

1196.2 

2.532 

.3949 

180 

182 

374.0 

346.4 

850.0 

1196.4 

2.506 

.3990 

182 

184 

374.9 

347.4 

849.3 

1196.7 

2.480 

.4032 

184 

186 

375.8 

348.3 

848.5 

1196.8 

2.455 

.4074 

186 

188 

376.7 

349.2 

847.7 

1196.9 

2.430 

.4115 

188 

190 

377.6 

350.1 

847.0 

1197.1 

2.406 

.4157 

190 

192 

378.5 

351.0 

846.2 

1197.2 

2.381 

.4200 

192 

194 

379.3 

351.9 

845.5 

1197.4 

2.358 

.4242 

194 

196 

380.2 

352.8 

844.8 

1197.6 

2.335 

.4284 

196 

198 

381.0 

353.7 

844.0 

1197.7 

2.312 

.4326 

198 

200 

381.9 

354.6 

843.3 

1197.9 

2.289 

.4370 

200 

202 

382.7 

355.5 

842.6 

1198.1 

2.268 

.4411 

202 

204 

383.5 

356.4 

841.9 

1198.3 

2.246 

.4452 

204 

206 

384.4 

357.2 

841.2 

1198.4 

2.226 

.4493 

206 

208 

385.2 

358.1 

840.5 

1198.6 

2.206 

.4534 

208 

210 

386.0 

358.9 

839.8 

1198.7 

2.186 

.4575 

210 

212 

386.8 

359.8 

839.1 

1198.9 

2.166 

.4618 

212 

214 

387.6 

360.6 

838.4 

1199.0 

2.147 

.4660 

214 

216 

388.4 

361.4 

837.7 

1199.1 

2.127 

.4700 

216 

218 

389.1 

362.3 

837.0 

1199.3 

2.108 

.4744 

218 

220 

389.9 

363.1 

836.4 

1199.5 

2.090 

.4787 

220 

222 

390.7 

363.9 

835.7 

1199.6 

2.072 

.4829 

222 

224 

391.5 

364.7 

835.0 

1199.7 

2.054 

.4870 

224 

226 

392.2 

365.5 

834.3 

1199.8 

2.037 

.4910 

226 

228 

393.0 

366.3 

833.7 

1200.0 

2.020 

.4950 

228 

230 

393.8 

367.1 

833.0 

1200.1 

2.003 

.4992 

230 

232 

394.5 

367.9 

832.3 

1200.2 

1.987 

.503 

232 

234 

395.2 

368.6 

831.7 

1200.3 

1.970 

.507 

234 

236 

396.0 

369.4 

831.0 

1200.4 

1.954 

.511 

236 

238 

396.7 

370.2 

830.4 

1200.6 

1.938 

.516 

238 

240 

397.4 

371.0 

829.8 

1200.8 

1.923 

.520 

240 

242 

398.2 

371.7 

829.2 

1200.9 

1.907 

.524 

242 

244 

398.9 

372.5 

828.5 

1201.0 

1.892 

.528 

244 

246 

399.6 

373.3 

827.8 

1201.1 

1.877 

.532 

246 

248 

400.3 

374.0 

827.2 

1201.2 

1.862 

.537 

248 

250 

401.1 

374.7 

826.6 

1201.3 

1.848 

.541 

250 

275 

409.6 

383.7 

819.0 

1202.7 

1.684 

.594 

275 

300 

417.5 

392.0 

811.8 

1203.8 

1.547 

.647 

300 

350 

431.9 

407.4 

798.5 

1205.9 

1.330 

.750 

350 

STEAM  29 

2.  Temperatures  of  saturated  steam  in  degrees  Fahrenheit  (t). 
This  column  of  temperatures  shows  the  vaporization  tempera- 
ture, or  the  boiling  point,  at  each  of  the  given  pressures. 

3.  Heat  of  the  liquid  (h),  or  the  heat  required  to  bring  up 
the  temperature  of  a  pound  of  water  from  freezing  point  to  boiling 
point  at  the  given  pressure. 

4.  The  latent  heat  (L),  or  the  heat  required  to  vaporize  a 
pound  of  water  into  dry  steam  at  the  given  pressure,  after  the 
boiling  point  is  reached. 

5.  The  total  heat  of  the  steam  (H),  which  is  the  sum  of  the 
heat  of  the  liquid  and  the  latent  heat,  and  represents  the  total  heat 
that  is  required  to  generate  dry  saturated  steam  from  water  at  the 
freezing  point,  at  the  various  pressures. 

6.  The  volume  of  1  pound  of  dry  steam  (v)  at  the  various 
pressures. 

7.  Density  of  dry  steam  in  pounds  per  cubic  foot  (- )  • 

To  illustrate  the  use  of  the  steam  tables  the  following  examples 
will  be  solved: 

Example  1. — Water  at  200°F.  is  fed  to  a  boiler  in  which  the  pressure  is 
100  pounds  per  square  inch  gage.  How  much  heat  must  be  supplied  by  the 
fuel  to  evaporate  each  pound  of  water  into  dry  steam  ? 

Solution. — A  pressure  of  100  pounds  per  square  inch  gage  =  100  +  14.7 
=  114.7  pounds  per  square  inch  absolute,  if  the  barometer  reading  is  30 
in. 

The  heat  required  to  evaporate  one  pound  of  water  from  freezing  point 
into  dry  steam  at  a  pressure  of  114.7  lb.  per  square  inch  absolute  is  the 
total  heat  of  steam  (H)  at  the  pressure,  or  1188.6. 

Since  the  water  fed  to  the  boiler  has  a  temperature  of  200°F.,  the  total 
amount  of  heat  to  be  supplied  by  the  fuel  to  evaporate  one  pound  of  water 
into  dry  steam  is: 

1 188.6  -  (200  -  32)  =  1020.6  B.t.u. 

Example  2. — If  the  steam  in  example  1,  contained  3  per  cent,  moisture, 
calculate  the  heat  which  must  be  supplied  by  the  fuel  to  evaporate  each 
pound  from  feed  water  at  200°F. 

Solution. — The  heat  of  the  liquid,  or  the  heat  required  to  raise  the  tem- 
perature of  a  pound  of  water  from  200°F.  to  the  boiling  point  corresponding 
to  a  pressure  of  114.7  pounds  per  square  inch  absolute  is: 
308.8  -  (200  -  32)  =  140.8  B.t.u. 

The  heat  required  to  vaporize  a  pound  of  water  into  dry  steam  at  114.7 
pounds  per  square  inch  absolute,  after  the  boiling  point  is  reached,  is  879.8 
B.t.u. 


30         STEAM  AND  GAS  POWER  ENGINEERING 

Since  the  steam  in  this  example  contains  3  per  cent  moisture,  it  is  97  per 
cent,  dry,  and  the  heat  required  to  vaporize  it  is : 
879.8  X  0.97  =  853.4  B.t.u. 
The  total  heat  required  to  change  one  pound  of  water  at  200°  F.  into 
steam,  3  per  cent,  wet,  and  at  a  pressure  of  114.7  pounds  per  square  inch 
absolute  is : 

140.8  +  853.4  =  994.2  B.t.u. 
Example  3. — What  is  the  volume  of  one  pound  of  steam  at  150  lbs.  per 
square  inch  absolute,  if  it  is  20  per  cent,  wet? 

Solution. — Dry  steam  at  a  pressure  of  150  lbs.  per  sq.  in.  absolute  has  a 
volume  of  3.013  cu.  ft.  per  pound. 

The  volume  of  one  pound  of  steam  which  is  20  per  cent,  wet,  or  80  per 
cent,  dry,  at  a  pressure  of  150  pounds  per  square  inch  absolute  is: 
3.013  X  0.80  =  2.41  cubic  feet. 

Determination  of  the  Quality  of  Steam.— The  quality,  or  the 
per  cent,  of  moisture  in  saturated  steam,  is  determined  by  means 
of  a  calorimeter.  There  are  three  types  of  steam  calorimeters 
in  general  use,- — the  Throttling  Calorimeter,  the  Separating 
Calorimeter,  and  the  Electrical  Calorimeter. 

The  throttling  calorimeter  is  the  most  accurate  instrument 
for  measuring  the  amount  of  moisture  in  steam.  This  instrument 
depends  for  its  action  upon  the  fact  that  steam,  nearly  dry, 
becomes  superheated  when  its  pressure  is  reduced  by  throttling, 
since  saturated  steam  at  high  pressure  contains  more  heat  than 
at  low  pressure.  A  simple  type  of  throttling  calorimeter  is 
illustrated  in  Fig.  6.  0  is  the  orifice  discharging  into  the  chamber 
C,  into  which  a  thermometer  T  is  inserted.  A  mercury  manome- 
ter is  attached  at  Vs. 

Let  Pi  equal  the  absolute  pressure  of  the  steam  in  the  main 
steam  pipe.  The  heat  contained  in  one  pound  of  steam  at  the 
pressure  Pi  would  be  the  sum  of  the  heat  of  the  liquid  (hi)  and 
the  latent  heat  of  steam  (Lx)  corrected  for  the  moisture,  or 

hi  +  xLi 

where  x  is  the  quality  of  the  steam. 

If  the  steam  has  a  pressure  P2,  as  indicated  by  the  manometer, 
attached  to  Vz,  after  it  passes  the  orifice  0,  and  a  temperature 
ts,  as  registered  by  the  thermometer  T,  the  heat  contained 
in  one  pound  of  steam  at  the  pressure  P2  would  be  the  total 
heat  (Hz)  of  dry  saturated  steam  at  the  lower  pressure  plus  the  heat 


STEAM 


31 


due  to  the  superheat.  The  heat  due  to  the  superheat  is  calcu- 
lated by  multiplying  the  degrees  of  superheat  by  the  specific 
heat  of  superheated  steam  at  the  given  pressure  and  temperature. 
By  specific  heat  is  meant  the  resistance  which  a  substance  offers 
to  a  change  in  its  temperature.  The  average  value  of  the  specific 
heat  of  superheated  steam  (CP)  at  the  temperatures  and  pressures 
common  in  calorimeters  is  0.4,7.  The  degrees  of  superheat 
are  determined  by  subtracting  the  saturated  temperature  (t2) 
corresponding    to    the    lower    pressure,    as    measured    by  the 


Fig.  6. — Throttling  steam  calorimeter. 


manometer  at  Vz,  from  the  temperature  t8,  as  indicated  by  the 
thermometer  T  of  the  steam  calorimeter. 

Since  the  total  heat  in  the  steam  is  the  same  on  both  sides 
of  the  calorimeter: 

hi  +  xU  =  H2  +  0.47ft,  -  h) 
Solving  for  x,  the  quality  of  steam  is  calculated  as  follows : 
#2  +  0.47  (t,  -  U)  -  ^ 


x  = 


u 


32         STEAM  AND  GAS  POWER  ENGINEERING 

Example. — Steam  is  tested  by  means  of  a  throttling  calorimeter.  Find 
the  per  cent,  of  moisture  in  the  steam  if  the  gage  pressure  of  the  3team  in  the 
main  steam  pipe  is  115.3,  the  pressure  in  the  calorimeter,  as  indicated  by  the 
manometer  at  Vz  (Fig.  6),  two  inches  of  mercury,  and  the  temperature  of 
the  calorimeter  thermometer  at  T  (Fig.  6)  260°F. 

Solution. — Pi   =  115.3  +  14.7  =  130  pounds  per  square  inch  absolute. 
h  =  318.6 
Li  -  872.2 
P2  =  14.7  +  (2  X  0.491)  =  15.68.     (One  inch  of  mercury  is 

equal  to  0.491  pounds  pressure  per  square  inch.) 
H2  =  1151.4 
t2  =  215.3 

_  1151.4  +  0.47  (260  -  215.3)  -  318.6 
x  -  g^^  -  °-978 

Per  cent,  of  moisture  =  100  —  97.8  =  2.2 

The  throttling  calorimeter  is  unsuitable  for  measuring  the 
quality  of  steam  which  contains  more  than  3  or  4  per  cent, 
moisture. 

The  amount  of  moisture  in  very  wet  steam  can  best  be  deter- 
mined by  a  separating  calorimeter,  illustrated  in  Fig.  7.  Steam 
enters  the  separating  calorimeter  at  A  (Fig.  7),  passes  down  the 
vertical  pipe,  plugged  at  the  lower  end,  from  which  it  escapes 
through  a  large  number  of  holes  as  indicated.  The  moisture  col- 
lects at  the  bottom  of  the  vessel  V  and  can  be  measured  by  the 
calibrated  glass  gage  G.  The  steam  leaves  the  calorimeter  at  N 
and  can  be  collected,  condensed  and  weighed.  The  gage  P 
indicates  the  pressure  in  the  jacket  J.  This  pressure  is  roughly 
proportional  to  the  flow  of  steam  through  the  nozzle  N.  The 
gage  P  is  usually  provided  with  a  scale  to  indicate  the  approxi- 
mate flow  of  steam.  The  per  cent,  of  moisture  is  calculated 
by  dividing  the  weight  of  water  collected  in  the  gage  glass  G 
by  the  sum  of  the  weights  of  steam  passing  out  at  N  and  of  the 
water  at  G. 

The  electrical  calorimeter  consists  of  an  electric  heater  which 
is  used  for  drying  and  for  superheating  the  steam.  The  amount 
of  electric  energy  required  to  dry  the  steam  is  proportional  to 
the  amount  of  moisture  in  the  steam. 

Problems 
1.  A  boiler  generates  steam  at  a  pressure  of  120  pounds  by  the  gage.     If 
the  barometric  pressure  is  28.5  in.,  calculate  the  absolute  pressure  in  pounds 
per  square  inch. 


STEAM 


33 


2.  Calculate  the  heat  required  to  change  20  pounds  of  water  at  a  tempera- 
ture of  190°F.  into  dry  steam  at  150  pounds  per  square  inch  absolute. 

3.  If  the  steam  in  problem  2  contains  5  per  cent,  moisture,  calculate  the 
heat  required. 

4.  Compare  the  volumes  of  one  pound  of  steam  at  the  following  pressures 
in  pounds  per  square  inch  absolute:  >£,  1,  2,  14.7,  100,  150,  200,  300. 


Fig.  7. —  Separating  calorimeter. 


5.  A  plain  cylindrical  boiler  has  a  diameter  of  30  inches  and  a  length  of 
12  feet.  If  two-thirds  of  the  volume  of  the  boiler  is  filled  with  water  at  a 
temperature  of  270°F.,  the  other  third  with  steam,  calculate: 

(a)  Boiler  pressure  in  pounds  per  square  inch  gage  if  the  barometer  is 
29.2  inches. 
3 


34         STEAM  AND  GAS  POWER  ENGINEERING 

(b)  Calculate  the  weight  of  the  water  and  the  weight  of  the  steam,  con- 
tained in  the  boiler. 

6.  The  quality  of  steam  at  a  pressure  of  140  pounds  per  square  inch 
gage  is  measured  by  means  of  a  throttling  calorimeter.  If  the  calorimeter 
thermometer  reads  270°F.  and  the  manometer  registers  3  inches  of  mercury, 
calculate  the  quality  of  the  steam. 

7.  Prove  that  the  throttling  calorimeter  will  be  unsuitable  for  measuring 
the  quality  of  steam  which  has  10  per  cent,  moisture  at  a  steam  pressure  of 
150  pounds  per  square  inch  gage. 

8.  Steam  is  tested  by  means  of  a  separating  calorimeter  (Fig.  7)  and  gives 
the  following  results : 

Water  collected  in  the  glass  gage  G 0 .  25  lb. 

Steam  collected  at  iV 0. 90  lb. 

Calculate  the  quality  of  the  steam. 


CHAPTER  IV 
BOILERS 

The  function  of  a  boiler  is  to  generate  steam  to  be  used  either 
in  engine  cylinders,  or  for  heating  purposes.  The  term  boiler 
is  commonly  applied  to  the  combination  of  the  furnace  in  which 
the  fuel  is  burned  and  the  boiler  proper,  which  is  a  closed  vessel 
containing  water  and  steam. 

Classification  of  Boilers. — Boilers  are  divided  into  two  classes, 
the  fire-tube  and  the  water-tube.  In  the  fire-tube  boiler  (Fig.  9) 
the  hot  gases  developed  by  the  combustion  of  the  fuel  pass 
through  the  tubes,  while  in  the  water-tube  boiler  (Fig.  18)  these 
gases  pass  around  the  tubes.  Either  type  may  be  constructed 
as  a  vertical  or  as  a  horizontal  boiler,  depending  on  whether  the 
axis  of  the  shell  is  vertical  or  horizontal. 

The  fire-tube  boiler  may  be  externally  or  internally  fired.  In 
the  externally  fired  boiler  (Fig.  10)  the  furnace  is  in  the  brick 
setting  entirely  outside  of  the  boiler  shell,  while  in  the  internally 
fired  types  (Figs.  13  and  14)  the  furnace  is  in  the  boiler  shell, 
no  brick  setting  being  necessary.  For  stationary  work  the 
externally  fired  boiler  is  the  most  common,  while  the  internally 
fired  types  are  always  used  for  locomotive  and  traction  engine 
purposes,  and  generally  for  marine  power  plants.  Vertical 
fire-tube  boilers  are  usually  internally  fired. 

Plain  Cylindrical  Boiler. — The  plain  cylindrical  type  of  boiler 
is  practically  obsolete,  but  it  is  of  interest  because  of  its  simplicit}'. 
Fig.  8  illustrates  a  longitudinal  cross-section  of  such  a  boiler. 
It  consists  of  a  cylindrical  shell  closed  at  its  two  ends  by  dished 
heads.  Because  of  the  circular  shaped  heads,  no  staying  is 
necessary.  The  chief  disadvantage  in  the  use  of  this  type  of 
boiler  is  the  small  amount  of  heating  surface  it  contains,  which 
means  that  an  extremely  large  boiler  is  necessary  for  small 
evaporative  effects. 

35 


36 


STEAM  AND  GAS  POWER  ENGINEERING 


Horizontal  Return  Tubular  Boiler. — Boilers  of  this  type 
are  most  commonly  used  in  this  country.  They  are  simple, 
inexpensive,  have  a  large  overload  capacity,  and  are  economical 


r 


JX 


^^^^^^^^^l^^^^^^^^^^^^^ 


Fig.  8. — Plain  cylindrical  boiler. 

when  properly  handled.  The  general  appearance  of  a  return 
tubular  boiler  is  shown  in  Fig.  9.  Fig.  10  illustrates  the  details 
of  the  setting. 

These  boilers  consist  of  a  cylindrical  shell  closed  at  the  ends 


Return  tubular  boiler. 


by  two  flat  heads,  and  of  numerous  small  fire  tubes  which  extend 
the  whole  length  of  the  shell.  The  fire  tubes  are  three  or  four 
inches  in  diameter  and  14  to  18  feet  long.  About  two-thirds  of 
the  volume  of  the  shell  is  filled  with  water,  the  other  third, 


BOILERS 


37 


called  the  steam  space,  being  left  for  the  disengagement  of  the 
steam  from  the  water.  The  water  line  is  about  six  inches  above 
the  top  row  of  fire  tubes.     Sometimes,  as  shown  in  Fig.  11,  a 


Fig.  10. —  Details  of  boiler  setting. 

steam  dome  D  is  provided  to  increase  the  volume  of  the  steam 
space.  Steam  domes  are  seldom  used  in  modern  boilers  for 
stationary  power  plants,  as  they  weaken  the  boiler  shell  and  add 
to  the  first  cost  of  the  boiler. 


Fia.  11. — Boiler  with  dome. 


The  coal  is  burned  upon  the  grates  which,  as  shown  in  Fig.  10, 
rest  upon  the  bridge  wall  W  and  upon  the  front  of  the  setting. 
The  hot  gases,  formed  by  the  combustion  of  the  fuel,  pass  from 
the  furnace  under  and  along  the  boiler  shell  to  the  back  connec- 
tion, or  combustion  chamber  C,  from  there  to  the  front  through 


38 


STEAM  AND  GAS  POWER  ENGINEERING 


the  tubes,  and  up  the  uptake  to  the  breeching  or  flue,  which  leads 
to  the  chimney. 

The  distance  between  the  grates  and  the  boiler  shell  should  be 
greater  for  bituminous  than  for  anthracite  coal.  This  distance, 
in  the  case  of  the  best  anthracite  coal,  may  be  as  little  as  24 
inches,  but  for  bituminous  coal  the  distance  between  the  grates 
and  the  boiler  should  be  more  than  36  inches.  The  greater  this 
distance  the  more  opportunity  will  be  given  for  the  proper  com- 
bustion of  the  fuel. 

This  type  of  boiler  is  usually  provided  with  a  hand-hole  or  a 
man-hole  in  front  below  the  tubes,  and  with  a  man-hole  in  the  top 
of  the  boiler. 


4      $ 


Triangular 
Loop 


Fig.  12. — Independent  method  of  setting  boiler. 


The  flat  heads,  or  tube  sheets  of  the  boiler,  are  stayed  below 
the  water  line  by  the  tubes.  Above  the  water  line  special  stays 
must  be  provided  to  prevent  the  tube  sheets  from  distorting. 
In  Fig.  9  the  distortion  of  the  tube  sheet  above  the  tubes  is  pre- 
vented by  the  use  of  diagonal  stays  which  transfer  the  strain  to 
the  shell  of  the  boiler. 

Boilers  of  this  type  are  usually  set  in  brick  settings.  In  some 
cases  the  boiler  is  supported  by  brackets,  as  shown  in  Fig.  10. 
In  this  case  the  front  brackets  rest  on  metal  plates  embedded  in 
the  brickwork  of  the  side  walls,  while  the  back  brackets  are  placed 
on  rollers,  which  in  turn  rest  on  horizontal  plates,  this  method 
allowing  the  back  of  the  boiler  to  move  as  the  shell  expands  or 


BOILERS  39 

contracts.  A  better  method  is  to  support  the  boiler  independent 
of  the  setting,  on  steel  framework,  as  shown  in  Fig.  12. 

The  setting  should  be  constructed  so  that  the  hot  gases  will  not 
come  in  contact  with  the  shell  above  the  water  line. 

Scotch  Marine  Boiler. — -A  single  ended,  two  furnace  Scotch 
marine  boiler  is  shown  in  Fig.  13.  This  boiler  differs  from 
those  previously  described  in  that  it  is  internally  fired.  The 
boiler  consists  of  a  cylindrical  shell  enclosed  at  its  two  ends 
by  flat  plates.  The  furnace  flues  are  connected  to  a  combus- 
tion chamber.  Numerous  fire  tubes  fill  the  upper  portion  of  the 
boiler.  The  travel  of  gases  is  first  through  the  furnace-flues, 
then  to  the  combustion  chamber,  and  finally  through  the  tubes 
to  the  uptake  and  stack. 

Boilers  of  this  type  are  self  contained,  require  little  overhead 
room,  and  no  setting.  The  rear  surface  of  the  combustion  cham- 
ber is  stayed  by  connecting  it  to  the  rear  head  by  means  of  short 
bolts,  termed  stay  bolts.  The  front  surface  of  the  combustion 
chamber  is  stayed  by  the  furnace  flues  and  the  tubes,  while  the 
top  of  the  chamber  is  supported  by  a  bar  which  transmits  the 
strain  to  the  two  side  sheets  and  is  termed  a  girder  stay.  The 
heads  of  the  boiler  above  the  tubes  are  supported  by  through 
stays,  which  are  rods  connecting  both  heads  as  shown.  Large 
boilers  of  this  type  are  provided  with  furnaces  at  both  ends 
which  open  into  a  common  combustion  chamber  in  the  middle 
of  the  boiler. 

Locomotive  Boiler. — Fig.  14  illustrates  a  locomotive  boiler. 
A  type  similar  to  the  one  shown  is  used  in  stationary  work. 
The  stationary  type,  however,  is  only  made  in  comparatively 
small  sizes  and  finds  its  application  only  in  isolated  locations,  or 
where  steam  is  required  temporarily.  The  type  used  in  loco- 
motive practice  as  well  as  that  used  in  stationary  work  is  classified 
as  a  fire-tube,  internally  fired  boiler. 

The  locomotive  boiler  consists  of  a  cylindrical  shaped  barrel 
or  shell  which  contains  a  large  number  of  fire-tubes.  The 
furnace  or  fire-box  is  constructed  by  extending  the  shell  down- 
ward to  form  the  sides.  The  walls  of  the  fire-box  are  made 
double,  the  space  thus  created  being  connected  to  the  water  space 
in  the  shell.  This  extension  of  the  plates  to  form  the  sides  of  the 
fire-box  produces  two  narrow  sections  which  are  filled  with  water, 


40 


STEAM  AND  GAS  POWER  ENGINEERING 


BOILERS 


41 


forming  what  is  usually 
termed  a  water  leg.  These 
boilers  are  constructed  with 
a  steam  dome  from  which 
the  steam  is  taken. 

The  hot  gases  leave  the 
furnace,  pass  through  the 
small  tubes  to  the  smoke 
box  at  the  front  of  the 
boiler,  and  from  there  to 
the  stack. 

The  flat  sheets  compos- 
ing the  water  legs  are 
stayed  by  the  use  of  small 
stay  bolts.  The  same 
method  of  staying  is  ap- 
plied to  the  sheet  forming 
the  top  of  the  fire  box, 
but  in  this  case  the  name 
" crown  stays"  is  usually 
applied. 

Vertical  Fire-tube  Boil- 
ers.— Two  forms  of  vertical 
boilers  are  shown  in  Figs. 
15  and  16.  In  the  form 
shown  in  Fig.  15  the  tops 
of  the  tubes  are  above  the 
water  line,  and  may  become 
overheated  when  the  boiler 
is  forced.  To  prevent  in- 
jury from  this  cause,  some 
forms  of  vertical  boilers  are 
constructed  as  shown  in 
Fig.  16,  the  tops  of  the 
tubes  being  ended  in  a  sub- 
merged tube  sheet,  which 
is  kept  below  the  water 
line. 

The  essential  parts  of  all 
forms  of  vertical  boilers 
are  a  cynndrical  shell  with 
a  fire-box  and  ash  pit  in 


42 


STEAM  AND  GAS  POWER  ENGINEERING 


the  lower  end.  The  tubes  lead  directly  from  the  furnace  to 
the  upper  head  of  the  shell.  The  hot  gases  from  the  furnace 
pass  through  the  tubes  and  out  of  the  stack. 

Vertical  boilers  occupy  little  floor  space,  require  no  setting 
except  a  light  foundation,  and  are  inexpensive.  To  offset 
these  advantages,  vertical  boilers,  as  ordinarily  constructed,  are 


Fig.  15. 


-Vertical  boiler  exposed 
tube  type. 


Fig.  16. 


Vertical  boiler  submerged 
tube  type. 


uneconomical,  have  small  capacity,  have  too  little  space  for  the 
disengagement  of  the  steam,  and  are  inaccessible  for  thorough 
inspection  and  cleaning. 

Fig.  17  illustrates  one  of  the  larger  vertical  boilers,  known  as 
the  Manning  type.  The  tubes  in  this  boiler  are  much  longer 
than  those  usually  installed  in  vertical  boilers  of  the  types  pre- 
viously discussed,  consequently  the  heating  surface  is  greatly 
increased.  The  shell  is  enlarged  at  the  fire-box  to  provide  for  a 
larger  furnace  and  more  grate  area.     No  staying  is  required  in 


BOILERS  43 

this  boiler  except  at  the  water  leg,  and  at  this  point  the  inner 
sheet  of  the  fire-box  is  joined  to  the  outer  shell  by  stay  bolts. 


<-..._ 
^^^^■1 


Fig.  17. — Manning  vertical  boiler. 


Water  Tube  Boilers. — Water  tube  boilers  are  used  in  large 
power  plants  on  account  of  their  adaptability  to  higher  steam 


44 


STEAM  AND  GAS  POWER  ENGINEERING 


pressures  and  larger  sizes,  decreased  danger  from  serious  explo- 
sions, greater  space  economy,  and  rapidity  of  steam  generation. 
For  small  power  plants  and  for  steam  pressures  of  125  pounds  or 
less  the  fire  tube  boiler  is  usually  more  suitable  on  account  of  its 
lower  first  cost.  Also  in  a  fire-tube  boiler,  if  a  tube  should  break, 
the  boiler  can  be  repaired  by  plugging  without  seriously  interrupt- 
ing service,  which  is  not  the  case  with  most  types  of  water  tube 


Fig.  18. — Babcock  and  Wilcox  Boiler. 


boilers.  As  far  as  efficiency  is  concerned,  numerous  tests  show 
that  either  type,  when  properly  designed  and  operated,  will  give 
the  same  economy. 

There  are  many  different  types  of  water  tube  boilers,  but  the 
essential  parts  of  all  are  much  the  same.  They  consist  of  nu- 
merous tubes  filled  with  water,  and  one  or  more  drums  for  the  dis- 
engagement of  the  steam  from  the  water.     No  tubes  run  through 


BOILERS  45 

the  drums,  consequently  dished  heads  may  be  used,  thus  elimi- 
nating the  necessity  for  staying. 

The  Babcock  &  Wilcox  Boiler.- — Fig.  18  shows  the  Babcock 
and  Wilcox  type  of  water  tube  boiler.  This  boiler  consists  of 
a  number  of  straight  tubes  fastened  into  several  sets  of  headers 
which  are  connected  to  a  common  drum.  The  feed  water  enters 
the  boiler  through  a  pipe  passing  through  the  front  end  of  the 
drum  and  extending  back  about  one-third  of  its  length.  Oppo- 
site the  end  of  each  tube  there  is  provided  a  hand  hole  through 
which  the  tubes  may  be  inspected  or  cleaned.  The  hot  gases  from 
the  furnace  are  deflected  by  means  of  fire  brick  baffle  plates  and 
the  bridge  wall  and  pass  across  the  tubes  three  times  before  reach- 
ing the  uptake  at  the  rear  of  the  boiler.  In  some  cases  the  baffling 
is  arranged  so  that  the  gases  are  directed  along  the  tubes.  The 
boiler  is  supported  by  steel  beams  resting  on  columns  independent 
of  the  setting. 

The  Heine  Boiler. — The  Heine  boiler  is  illustrated  in  Fig.  19. 
It  consists  of  a  number  of  straight  tubes,  expanded  into  two  water 
legs  or  headers  of  flanged  steel  plate,  which  are  connected  to  a 
common  drum.  The  tubes  are  parallel  to  the  drum.  Opposite 
the  end  of  each  tube  is  a  hand  hole  to  facilitate  cleaning  and  in- 
spection. The  feed  water  enters  the  boiler  through  the  front 
head,  passes  into  a  mud  drum,  where  the  impurities  are  deposited, 
circulates  from  the  front  toward  the  back  in  the  drum,  and  from 
the  back  toward  the  front  in  the  tubes.  The  baffle  plates  in 
this  type  of  boiler  are  usually  arranged  horizontally  so  that  the 
hot  gases  pass  first  to  the  rear  of  the  boiler,  then  back  through 
the  nest  of  tubes  to  the  front,  and  finally  back  to  the  stack, 
coming  in  contact  with  the  drum  of  the  boiler  in  this  last  pass. 
This  boiler  is  supported  independently  of  the  setting  at  the  front 
end,  while  the  rear  water  leg  rests  upon  the  rear  wall. 

Stirling  Boiler. — Fig.  20  shows  a  sectional  elevation  of  a  Stirling 
water  tube  boiler.  This  boiler  consists  of  four  horizontal  cylin- 
drical drums,  three  at  the  top  and  one  large  drum  at  the  bottom. 
A  series  of  inclined  water  tubes  connect  the  upper  drums  with  the 
lower.  Tubes  are  used  to  connect  the  steam  spaces  of  the  upper 
drums  so  that  any  steam  formed  in  these  may  be  transmitted  to 
the  middle  drum.  Similarly  a  series  of  tubes  connects  the  front 
and  middle  drums  below  the  water  line.     Such  a  connection 


46 


STEAM  AND  GAS  POWER  ENGINEERING 


limits  the  main  circulation  within  the  boilers  to  the  front  and 
middle  bank  of  tubes. 

The  feed  water  enters  the  rear  upper  drum,  flows  downward 
through  the  rear  bank  of  tubes  to  the  bottom  drum,  where  the  im- 
purities are  deposited,  and  then  upward  through  the  front  bank 
of  tubes.     The  rear  system  of  tubes  acts  as  a  feed  water  heater. 


Fig.  19.— Heine  boiler. 


The  steam  formed  during  the  passage  upward  through  the  front 
tubes  becomes  separated  from  the  water  in  the  front  drum  and 
passes  into  the  middle  drum,  which  is  connected  with  the  steam 
main.  The  safety  valve  is  located  on  the  top  of  the  middle  drum. 
The  baffle  walls  are  set  so  that  the  hot  gases  from  the  furnace 
pass  over  the  bridge  wall,  and  thence  upward  through  the  first 


BOILERS 


47 


bank  of  tubes.  It  then  passes  downward  through  the  second 
set  of  tubes,  and  finally  upward  through  the  remaining  set  to 
the  stack.  Thus  the  water  and  hot  gases  circulate  in  opposite 
directions. 

Wickes  Boiler. — Fig.  21  illustrates  the  Wickes  vertical  water 
tube    boiler.     This  boiler  consists  primarily  of   two   cylinders 


Stirling  water  tube  boiler. 


joined  together  by  straight  tubes.  The  tubes  are  divided  into 
two  sets  by  a  baffle  wall  which  passes  through  their  center.  The 
whole  boiler  is  erected  in  a  vertical  position  and  is  surrounded 
by  brickwork. 

The  gases  generated  in  the  furnace  pass  upward  through  the 
forward  compartment,  and  are  directed  downward  through  the 
rear  compartment.  The  hotter  gases  thus  come  in  contact  with 
the  front  tubes,  while  the  cooler  gases  surround  those  at  the  rear. 


48 


STEAM  AND  GAS  POWER  ENGINEERING 


This  causes  the  main  circulation  within  the  boiler  to  be  upward 
through  the  front  and  downward  through  the  rear  compartment. 
Parker  Down  Flow  Boiler. — The  Parker  boiler  is  illustrated  in 
Fig.  22,  and  consists  of  a  cylindrical  drum  inside  of  which  is  a 
diaphragm  separating  the  steam  space  from  the  water  space. 


Fig.  21. — Wickes  vertical  boiler. 


The  tubes  are  arranged  to  form  a  series  of  continuous  passages, 
termed  elements,  leading  downward  from  the  water  chamber,  and 
are  finally  directed  upward  from  the  bottom  ends  to  the  steam 
chamber.  A  check  valve  at  the  top  of  each  element  prevents  the 
reversal  of  flow.  The  straight  tubes  form  the  continuous  ele- 
ments by  expanding  them  into  junction  boxes,  which  are  pro- 
vided with  a  hand-hole  opening  opposite  each  tube. 


BOILERS 


49 


The  water  fed  into  the  drum  seeks  its  level  in  the  elements. 
When  heat  is  applied  the  water  in  the  elements  is  soon  discharged 
as  steam,  into  the  drum.  The  water  then  runs  down  from  the 
drum  in  an  effort  to  retain  its  level  which  is  made  impossible 
by  the  continuous  evaporation.  As  a  result,  there  is  a  rapid 
flow  of  water  and  steam  downward  through  the  tube  elements 
impelled  by  the  gravity  head  of  water. 


Fig.  22. — Parker  down-flow  boiler. 

The  locations  of  the  tube  elements  and  of  the  baffle  walls  are 
arranged  in  such  a  manner  that  the  gases  and  water  circulate 
in  opposite  directions.  This  principle  brings  the  hottest  steam 
in  contact  with  highly  heated  gases,  and  steam  at  the  lower  tem- 
perature in  contact  with  cooler  gases. 

This  boiler  as  in  the  case  of  most  of  the  others  of  the  water- 
tube  type  is  supported  independently  of  the  boiler  setting. 

Marine  Water  Tube  Boilers. — The  service  to  which  a  boiler 
is  to  be  applied  modifies  its  design.  Several  types  of  water 
tube  boilers  have  been  designed  and  have  been  found  well  adapted 
to  marine  work.     The  main  requirements  for  a  successful  boiler  in 


50 


STEAM  AND  GAS  POWER  ENGINEERING 


this  class  of  service  are  that  it  should  occupy  little  space  and 
have  a  large  evaporative  capacity. 

Fig.    23   illustrates  a  water-tube  boiler  of  the  Babcock  and 
Wilcox   type,    designed   for   marine   service.     It   consists   of    a 


Fig.  23. — Babcock  and  Wilcox  Marine  boiler. 


cylindrical  drum  whose  axis  is  at  right  angles  to  those  of  the 
tubes,  or  is  crossed.  The  tubes  are  connected  to  headers,  but 
the  size  of  these  tubes  is  smaller  and  the  number  of  them  larger 
than  is  common  in  the  stationary  type. 

Materials.- — Boilers  intended  for  power  purposes  are  made  of 


BOILERS  51 

rolled  steel  plates  riveted  together.  Steel  is  the  most  desirable 
material  for  the  construction  of  a  boiler  because  of  its  strength 
and  cheapness,  and  also  because  of  its  ductility,  which  permits 
the  material  to  be  formed  into  the  irregular  shapes  necessary 
in  constructing  the  boiler.  Boiler  tubes  are  made  of  steel  and 
are  usually  lap  welded. 

Cast  iron  is  not  generally  considered  a  suitable  material.  It  is 
brittle,  possesses  practically  no  ductility,  and  often  produces 
unsound  castings.  It  is  used  only  in  the  construction  of  house 
heating  boilers,  as  in  this  class  of  service  high  pressures  are  not 
necessary. 

Copper  is  used  in  boiler  construction  in  special  cases,  as  in  fire 
engine  boilers,  where  the  use  of  a  material  of  less  strength  and 
greater  cost  is  permissible  in  order  to  obtain  a  quick  steaming 
boiler. 

Heating  Surface. — The  heating  surface  of  a  boiler  is  that 
surface  which  is  exposed  to  the  flame  and  hot  gases.  This 
term  is  expressed  in  square  feet,  and  the  general  rule  employed  in 
its  calculation  is  to  measure  that  part  of  the  surface  which  is  in 
contact  with  the  flame  or  gases.  For  example,  the  heating 
surfaces  of  a  boiler  tube  would  be  calculated  by  multiplying  the 
internal  circumference  of  the  tube  in  feet  by  its  length  in  feet  if 
the  tube  was  surrounded  by  water  upon  its  external  surface,  and 
its  internal  surface  was  in  contact  with  hot  gases,  as  is  the  case 
in  fire-tube  boilers.  If  this  condition  is  reversed,  as  is  the  case 
in  water-tube  boilers,  the  heating  surface  would  be  calculated  by 
multiplying  the  external  circumference  of  the  tube  by  its  length. 

In  a  horizontal  return  tubular  boiler,  the  heating  surface 
is  calculated  by  taking  two-thirds  of  the  cylindrical  surface 
of  the  shell,  adding  to  this  the  internal  area  of  all  the  tubes,  plus 
two-thirds  of  the  area  of  both  tube  sheets  and  subtracting  from 
the  result  twice  the  combined  external  cross-sectional  area  of  all 
the  tubes. 

The  heating  surface  of  a  boiler  is  proportional  to  its  capacity, 
or  to  the  ability  of  a  boiler  to  evaporate  water  into  steam.  The 
larger  the  quantity  of  water  to  be  evaporated  by  a  boiler,  the 
larger  must  be  its  heating  surface. 

Staying. — Cylindrical  or  spherical  surfaces  retain  their  shape 
when  subjected  to  either  a  bursting  or  to  a  collapsing  pressure. 


52  STEAM  AND  GAS  POWER  ENGINEERING 

Surfaces  having  a  flat  shape  tend  to  become  circular  or  spherical 
when  a  pressure  is  exerted.  This  tendency  of  flat  boiler  plates 
to  distort  when  pressure  is  applied  is  prevented  by  the  use  of 
stays,  as  was  pointed  out  in  connection  with  the  various  types  of 
boilers.  There  are  many  different  types  of  stays;  but  in  general 
they  consist  of  small  rods  which  connect  the  surfaces  to  be  stayed 
and  transfer  the  strain  either  to  the  shell  of  the  boiler  or  to  some 
other  surface.  These  stays  are  given  special  names,  depending 
upon  their  general  construction,  their  mode  of  connection,  or  the 
type  of  surface  to  which  they  are  best  suited. 

Settings  and  Furnaces. — In  building  a  boiler  setting  the  solid 
brick  wall  is  preferable  to  the  hollow  wall.  If  the  wall  is  built 
in  two  parts,  the  space  should  be  filled  with  ash,  crushed  brick  or 
sand,  as  loose  material  reduces  air  leakage  by  its  plasticity. 

Proper  furnace  design  will  aid  in  the  economical  combustion 
of  coal.  The  design  of  a  furnace  should  be  modified  to  suit  local 
fuels.  To  burn  coals  rich  in  volatile  matter,  the  furnace  must  be 
so  designed  that  the  gases  given  off  from  the  fuel  bed  remain  at  a 
high  temperature  until  the  combustion  process  is  complete. 
This  means  that  the  combustion  chamber  for  a  high  volatile 
coal  must  be  large  enough  for  the  air  to  mix  with  the  gases  given 
off  from  the  fuel  bed  and  before  such  gases  come  into  contact 
with  the  cool  heating  surfaces  of  the  boiler.  This  can  be  accom- 
plished by  the  use  of  an  extension  furnace,  such  as  the  Dutch 
oven  type,  or  by  having  the  heating  surfaces  elevated  at  a  con- 
siderable distance  above  the  grate.  The  more  volatile  matter 
the  coal  contains,  the  greater  should  be  the  distance  between  the 
grate  and  the  shell  or  the  tubes  of  the  boiler.  The  baffling  for 
water  tube  boilers  should  be  arranged  so  that  the  hot  gases  from 
the  fuel  bed  come  first  into  contact  with  the  baffles  at  the  bottom 
of  the  tubes. 

Air  infiltration  through  cracks  in  boiler  setting  reduces  the 
economy  of  a  boiler  plant.  Visible  cracks  in  the  setting  should 
be  covered.  The  practice  of  encasing  the  whole  setting  in  sheet 
steel,  or  the  application  of  asbestos  cement  on  the  outside  of  the 
setting,  should  be  employed  more  generally.  Radiation  losses 
can  be  reduced  by  the  use  of  insulating  brick. 

Sufficient  ash  pit  capacity  should  be  available  to  handle  the 
refuse  from  at  least  a  12-hour  run.     In  calculating  the  size  of  an 


BOILERS  53 

ash  pit,  the  weight  of  ashes  can  be  assumed  at  40  to  50  pounds 
per  cubic  foot.  In  plants  where  the  ashes  have  to  be  handled 
by  hand,  it  is  important  that  the  ash  pit  be  so  arranged  as  to 
be  readily  cleaned. 

Capacity  and  Efficiency  of  Steam  Boilers. — Boilers  are  usually 
rated  in  horsepower.  The  term  horsepower  in  this  connection 
is  only  a  matter  of  convenience,  and  does  not  mean  the  rate  of 
doing  work;  boiler  horsepower  is  an  arbitrary  unit  which  is  applied 
to  the  evaporation  of  a  definite  amount  of  water.  The  amount  of 
power  developed  by  a  steam  power  plant  per  unit  weight  of  steam 
generated  by  the  boiler  depends  upon  the  engine  used.  The 
American  Society  of  Mechanical  Engineers  has  recommended 
that  one  boiler  horsepower  should  mean  the  evaporation  of  30 
pounds  of  water  per  hour  at  100°F.  into  steam  at  70  pounds  gage. 
This  is  equivalent  to  the  evaporation  of  34J^  pounds  of  water  per 
hour  from  feed  water  at  212°F.  into  dry  steam  at  the  same 
temperature. 

Another  method  of  expressing  boiler  horsepower  is  in  terms 
of  heat.  To  evaporate  one  pound  of  water  from  a  temperature 
of  212°F.  into  steam  at  212°F.  only  the  latent  heat  of  evapora- 
tion at  that  temperature  is  required.  From  the  steam  tables 
page  24,  we  find  that  the  latent  heat  of  steam  at  212°F.  is  970.4 
B.t.u.  The  amount  of  heat  required  to  evaporate  34.5  pounds 
from  and  at  212°F.  would  be: 

34.5  X  970.4  =  33,479  B.t.u. 

Thus  a  boiler  horsepower  may  be  stated  as  the  absorption  by  the 
water  within  the  boiler  of  33,479  B.t.u.  per  hour. 

As  was  previously  mentioned,  the  capacity  of  a  boiler  depends 
upon  its  heating  surface.  Boiler  manufacturers  often  rate  boilers 
in  square  feet  of  heating  surface.  One  square  foot  of  boiler 
heating  surface  can  evaporate  economically  3  to  3.4  pounds  of 
water,  so  that  a  boiler  horsepower  can  be  produced  by  10  to  12 
square  feet  of  boiler  heating  surface.  For  fir  -tube  boilers  it  is 
customary  to  assume  10  to  12  square  feet  of  heating  surface  as 
representing  one  boiler  horsepower;  in  water-tube  boilers  10  square 
feet  of  heating  surface  is  equivalent  to  one  boiler  horsepower. 

The  following  example  will  illustrate  the  application  of  these 
terms: 


54         STEAM  AND  GAS  POWER  ENGINEERING 

Example. — A  boiler  evaporates  4,000  pounds  of  water  per  hour  into  dry 
steam  The  steam  pressure  is  100  pounds  per  square  inch  absolute,  and 
the  feed  water  enters  the  boiler  at  a  temperature  of  132°F  What  boiler 
horsepower  is  generated? 

Solution. — The  heat  required  to  evaporate  one  pound  of  the  water  under 
these  conditions  will  be  found  by  reference  to  the  steam  tables  page  26  to 
be 

1,186.2  -  (132  -  32)  =  1,086.2  B.t.u. 

The  total  heat  absorbed  by  the  water  per  hour  is 

4,000  X  1,086.2  =  4,344.800  B.t.u. 
Since  33,479  B.t.u.  is  the  rate  of  absorption  of  heat  per  boiler  horsepower, 
the  power  generated  by  the  boiler  is 

'  o  An      =  129.8  boiler  horsepower. 

Under  good  working  conditions,  a  boiler  will  evaporate  8 
to  12  pounds  of  water  per  pound  of  coal,  and  11  to  18  pounds  of 
water  per  pound  of  petroleum  fuel.  The  economy  of  a  boiler 
plant  depends  upon  the  quality  of  the  fuel  used,  the  design  of 
the  furnace  and  boiler,  the  condition  of  setting,  and  the  care  in 
firing. 

The  efficiency  of  a  boiler  is  the  ratio  of  the  heat  units  absorbed 
by  the  steam  per  pound  of  fuel  fired,  to  the  heat  units  supplied 
by  one  pound  of  the  fuel.  Tests  show  that  the  efficiencies  of 
boilers  will  vary  under  ordinary  working  conditions  from  about 
40  per  cent,  for  small  vertical  boilers  to  about  85  per  cent,  when 
well  designed  boilers  are  carefully  handled.  A  boiler  under  aver- 
age conditions  should  show  an  efficiency  of  about  70  per  cent. 
The  main  losses  in  a  boiler  are  the  heat  carried  away  by  the  flue 
gases,  the  loss  of  fuel  through  grates,  the  loss  due  to  poor  combus- 
tion of  the  fuel,  and  the  heat  lost  by  radiation. 

The  amount  of  heat  required  to  produce  one  pound  of  steam 
depends  upon  the  temperature  of  the  feed  water,  the  steam  pres- 
sure, and  the  quality  of  the  steam.  In  order  to  compare  boilers 
working  under  different  conditions,  the  economy  of  boilers  is 
expressed  as  the  equivalent  evaporation  from  and  at  212°F. 
This  means  that  the  actual  evaporation  per  pound  of  fuel  is 
reduced  to  the  number  of  pounds  of  water  which  would  be  evapo- 
rated if  the  feed  water  had  been  supplied  to  the  boiler  at  212°F., 
and  that  dry  steam  was  formed  at  that  temperature  which  is  the 
boiling  point  of  water  at  atmospheric  pressure. 


BOILERS  55 

Example. — A  boiler  generates  9  pounds  of  steam  per  pound  of  fuel  from 
feed  water  at  203°F.  Calculate  the  equivalent  evaporation  from  and  at 
212°F.,  if  the  steam  pressure  is  160  pounds  per  square  inch  absolute  and  the 
quality  steam  0.98  dry. 

Solution. — The  heat  required  to  evaporate  9  pounds  of  feed  water  at 
203°F.  into  steam  which  has  a  pressure  of  160  pounds  absolute  and  a  quality 
0.98  is  equal  to: 

9[335.5  -  (203  -  32)  +  0.98(858.8)]  =  9054.9  B.t.u. 
In  order  to  evaporate  water  at  212°F.  into  steam  at  the  same 
temperature,  970.4  B.t.u.  will  be  required,  therefore  the  equiva- 
lent evaporation  in  accordance  with  the  conditions  of  the  above 
problem  will  be: 

9054.9 


970.4 


=  9.33  lb. 


Firing. — To  the  average  person,  firing  consists  merely  of  open- 
ing the  furnace  door  and  throwing  fuel  on  the  grate.  This  is, 
however,  a  fallacy.  It  has  been  found  that  some  system  of  firing 
must  be  adopted  in  order  to  produce  economical  combustion  of 
coal.  The  method  to  be  adopted  depends  mainly  on  the  kind  of 
fuel  used. 

The  spreading  method  consists  of  distributing  a  small  charge 
of  coal  in  a  thin  layer  over  the  entire  grate.  This  system  of  firing 
will  give  satisfactory  results  with  anthracite  coal  and  with  some 
bituminous  coals.  With  this  method,  if  the  fuel  is  fed  in  large 
quantities  and  at  long  intervals,  incomplete  combustion  will 
result. 

The  alternate  method  consists  of  covering  first  one  side  of  the 
grate  with  fresh  fuel  and  then  the  other.  The  volatile  gases  that 
pass  off  from  the  fresh  fuel  on  one  side  of  the  grate  are  burned  with 
the  hot  air  coming  from  the  bright  side  of  the  fire.  This  system 
is  best  applied  to  a  boiler  with  a  broad  furnace. 

The  coking  method  is  best  adapted  for  the  smoky  and  for  the 
caking  varieties  of  bituminous  coal.  In  this  method  the  coal  is 
put  in  the  front  part  of  the  furnace,  and  allowed  to  remain  there 
until  the  volatile  gases  are  driven  off;  it  is  then  pushed  back  and 
spread  over  the  hot  part  of  the  furnace,  and  a  new  charge  is  thrown 
in  the  front. 

Either  one  of  the  three  systems  of  firing  explained  will  produce 
good  results,  if  properly  carried  out  and  if  the  fire  is  kept  bright 


56  STEAM  AND  GAS  POWER  ENGINEERING 

and  clean.  Smoke  indicates  incomplete  combustion  and  with 
bituminous  coal  occurs  if  the  volatile  gases  are  allowed  to  pass 
off  unburned. 

Management  of  Boilers. — Before  a  boiler  is  started  for  the 
first  time,  its  interior  should  be  carefully  cleaned,  care  being  taken 
that  no  oily  waste  or  foreign  material  is  left  inside  the  boiler. 
The  various  manholes  and  handholes  are  then  closed  and  the 
boiler  is  filled  to  about  two-thirds  of  its  volume  with  water. 
The  fire  is  started  with  wood,  oily  waste,  or  some  other  rapidly 
burning  materials,  keeping  the  damper  and  ashpit  door  open. 
The  fuel  bed  is  then  built  up  slowly. 

While  getting  up  the  steam  pressure,  the  water  gage  glass 
should  be  blown  out  to  see  that  it  is  not  choked,  the  gage  cocks 
should  be  tried,  and  all  auxiliaries  such  as  pumps,  injectors, 
pressure  gages,  piping,  etc.,  carefully  inspected.  The  safety 
valve  should  be  carefully  examined  and  tried  out  before  cutting 
the  boiler  into  service. 

When  cutting  a  boiler  into  service  with  others,  its  pressure 
should  be  the  same  as  that  of  the  other  boilers.  Steam  valves 
should  be  opened  and  closed  very  slowly  in  order  to  prevent 
water-hammer  and  stresses  from  rapid  temperature  changes. 

During  the  operation  of  a  steam  boiler  the  safety  valve  should 
be  kept  in  perfect  condition  and  tried  daily  by  allowing  the  pres- 
sure to  rise  gradually  until  the  valve  begins  to  simmer.  Each 
boiler  should  have  its  own  safety  valve  and  under  no  conditon 
should  a  stop  valve  be  placed  between  it  and  the  boiler.  The 
steam  gage  should  be  calibrated  from  time  to  time  with  a  stand- 
ard gage,  or  still  better  by  means  of  some  form  of  dead-weight 
tester.  It  is  best  not  to  depend  on  the  water  gage  glass  entirely. 
Gage  cocks  are  more  reliable  and  should  be  used  for  checking  the 
water  level  of  a  boiler. 

In  case  of  low  water,  do  not  turn  on  the  feed,  but  shut  the 
damper,  cover  the  fuel  bed  with  ashes,  or  if  that  is  not  available, 
with  green  coal.  The  safety  valve  should  not  be  lifted  until  the 
boiler  has  cooled  down,  as  an  explosion  may  occur.  Also  do  not 
change  operating  conditions  as  regards  the  use  of  steam.  If  the 
engine  is  running  allow  it  to  continue  but  do  not  open  valves  to 
reduce  the  pressure. 

A  boiler  should  be  cleaned  often  and  kept  free  from  scale. 


BOILERS  57 

If  water  free  from  impurities  is  used  a  boiler  may  be  run  several 
months  without  fear  of  serious  scale  formation,  but  in  most 
places  boilers  should  be  cleaned  at  least  once  a  month.  When 
preparing  to  clean  a  boiler,  allow  it  to  cool  down,  and  the  water 
to  remain  in  the  shell  until  you  are  ready  to  commence  cleaning. 

In  emergencies  split  tubes  of  fire-tube  boilers  may  be  plugged 
without  throwing  the  boiler  out  of  service.  Also  if  a  tube  becomes 
leaky  in  the  tube-sheet  the  fault  can  be  remedied  by  inserting  a 
tapering  sleeve  slightly  larger  than  the  inside  diameter  of  the 
tube. 

A  boiler  should  aways  be  thoroughly  inspected  before  it  is 
started.  In  the  case  of  the  locomotive  type  of  boiler  the  crown 
sheet  should  be  given  particular  attention. 

Problems 

1.  Calculate  the  heating  surface  of  a  fire-tube  boiler  to  which  you  have 
access,  after  taking  the  necessary  measurements. 

2.  Calculate  the  boiler  horsepower  of  the  boiler  in  Problem  1. 

3.  A  boiler  plant  operating  under  a  pressure  of  135  pound  per  sq.  in. 
gage  generates  18,000  pounds  of  saturated  steam  per  hour.  If  the  feed 
water  temperature  is  203° F.  and  the  quality  of  the  steam  3  per  cent,  wet, 
calculate  the  boiler  horsepower  of  the  plant. 

4.  Calculate  the  approximate  heating  surface  of  the  boiler  plant  in  Prob- 
lem 3,  assuming  fire-tube  boilers. 

5.  Prove  that  34>£  pounds  of  water  per  hour  from  and  at  212°F.  is  the 
same  as  the  evaporation  of  30  pounds  of  water  per  hour  from  feed  water  at 
100°F.  into  steam  at  70  pounds  gage  pressure. 

6.  Compare  the  equivalent  evaporation  from  and  at  212°F.  of  the  follow- 
ing boilers: 

Boiler  A  evaporates  1)4  pounds  of  water  per  hour  from  feed  water  at  140°- 
F.  and  into  steam  at  a  pressure  of  140  pounds  gage,  with  2  per  cent,  priming. 

Boiler  B  evaporates  S}4  pounds  of  water  per  hour  from  feed  water  at 
205°F.  and  into  steam  at  a  pressure  of  150  pounds  gage,  with  4  per  cent, 
priming. 

7.  Why  is  a  solid  wall  preferable  to  a  hollow  wall  for  a  boiler  setting? 

8.  Why  will  air  infiltration  through  cracks  in  a  boiler  setting  interfere 
with  the  economy  of  a  boiler  plant? 

9.  What  causes  a  boiler  to  explode? 

10.  Examine  some  power  plant  to  which  you  have  access  and  hand  in 
report  showing  the  following:  type  of  boilers  used,  steam  pressure  carried, 
methods  used  for  setting  boilers  (use  sketches),  and  temperature  of  feed 
water;  also  the  relation  between  the  rating  of  the  boilers  in  horsepower  and 
the  maximum  capacity  of  the  power  plant  in  horsepower  or  kilowatt. 


CHAPTER  V 

BOILER  AUXILIARIES 

Superheaters 

Types  of  Superheaters. — The  boilers  considered  in  the  last 
chapter  have  been  designed  for  the  generation  of  saturated 
steam.  Boilers  which  are  intended  for  superheated  service  must 
be  supplied  with  superheaters.  The  installation  of  a  superheater 
increases  the  amount  of  heat  available  in  the  boiler  plant  and 
makes  greater  economies  possible  in  the  utilization  of  the  steam 
in  steam  engines  and  in  steam  turbines.  Superheated  steam 
reduces  the  losses  of  heat  in  piping  systems,  as  superheated  steam 
gives  up  heat  less  readily  than  saturated  steam. 

The  cost  of  a  superheater  depends  upon  the  type  and  size, 
as  well  as  upon  the  degree  of  superheat  maintained.  Ordinarily 
the  installation  of  a  superheater  will  add  about  one-third  to  the 
cost  of  a  steam  boiler,  but  the  capacity  of  the  boiler  plant  will 
be  greatly  increased. 

Two  types  of  superheaters  are  used,  the  independently  fired 
and  the  attached  type.  The  independently  fired  superheater, 
as  its  name  indicates,  is  placed  in  an  independent  setting  and  is 
fired  by  a  separate  furnace.  The  attached  superheaters  are 
located  directly  in  the  boiler  setting,  or  in  the  flue  leading  from 
the  boiler,  derive  their  heat  from  the  same  furnace  as  the  boiler, 
and  are  consequently  subject  to  the  fluctuating  temperatures  of 
the  furnace.  In  the  independently  fired  superheater  the  degree 
of  superheat  is  independent  of  the  boiler  furnace.  By  means  of 
the  independently  fired  superheaters  higher  temperatures  are 
possible  than  with  the  attached  superheaters.  The  independ- 
ently fired  superheater  is,  however,  more  expensive  in  first  cost, 
costs  more  to  operate,  and  occupies  considerable  space,  as  com- 
pared with  the  attached  superheater. 

Practically  all  superheaters  consist  of  a  series  of  tubes  expanded 

58 


BOILER  AUXILIARIES 


59 


into  rectangular  steel  headers  through  which  the  steam  from  the 
boiler  passes  before  entering  the  piping  leading  to  the  engine. 
Heat  from  the  furnace  gases  is  thus  absorbed  by  the  flowing 
steam  and  its  temperature  is  raised  above  that  at  which  it  left 
the  boiler. 

To  prevent  a  superheater  from  overheating  some  provision  must 
be  made  to  protect  it  during  the  firing  up  of  the  boiler,  or  at 


Fig.  24. — Babcock  and  Wilcox  superheater. 

such  other  times  when  the  flow  of  steam  through  the  superheater 
is  small.  This  provision  has  given  rise  to  several  designs.  Super- 
heaters which  consist  of  plain  steel  tubes  in  contact  with  the  flue 
gases  at  all  times,  can  be  protected  by  flooding.  This  is  accom- 
plished by  allowing  water  to  pass  through  the  superheater  until  the 
steam  flow  is  at  such  a  rate  as  to  prevent  overheating.  Other  sup- 
erheaters are  protected  by  deflecting  the  furnace  gases  by  means 
of  dampers,  the  flow  of  gases  over  the  superheating  surface  being 


60 


STEAM  AND  GAS  POWER  ENGINEERING 


controlled  by  the  operator.  In  other  types,  the  tubes  are  pro- 
tected by  cast  iron  fins  or  rings  which  surround  each  tube.  Cast 
iron  is  capable  of  withstanding  higher  temperatures  than  steel; 
by  its  use  the  steel  tubes  are  protected  and  no  flooding  or  other 
protective  device  is  necessary. 

Babcock  &  Wilcox  Superheater. — Fig.  24  illustrates  a  Bab- 
cock  &  Wilcox  Superheater  attached  to  a  boiler  of  the  same  type. 


Stirling  boiler  with  attached  superheater. 


The  superheater  is  located  directly  under  the  boiler  drums  be- 
tween the  first  and  second  pass  of  the  boiler.  It  consists  of  a 
series  of  steel  tubes  expanded  into  steel  headers.  The  saturated 
steam  from  the  boiler  drum  enters  the  top  header  and  passes 
through  the  tubes  to  the  bottom  header.  The  superheated  steam 
is  conducted  from  the  bottom  header  to  the  main  piping. 

Stirling  Superheater. — Fig.  25  illustrates  a  Stirling  superheater 
attached  to  a  Stirling  boiler.     The  arrangement  of  this  boiler 


BOILER  AUXILIARIES 


61 


and  superheater,  differs  from  the  Stirling  boiler  for  saturated 
steam,  by  the  installation  of  the  superheater  in  place  of  the  mid- 
dle bank  of  tubes.  The  superheater  consists  of  two  drums  con- 
nected by  a  series  of  steel  tubes.  By  the  use  of  diaphragms  and 
valves  located  in  the  two  drums  the  steam  makes  a  circuitous 
path  through  the  superheating  elements.  This  superheater  is 
made  of  steel  tubes  which  are  in  the  path  of  the  furnace  gases, 
and  are  protected  from  overheating  by  flooding.  The  pipe  con- 
nection for  flooding  is  indicated  in  the  illustration  shown. 
Heine  Superheater. — The  Heine  superheater,  shown  in  Fig.  26, 


I 

B 

Jp-J:L— * 

Fig.  26. — Heine  superheater. 


differs  from  the  types  just  discussed  in  that  it  is  not  placed 
directly  in  the  path  of  the  flue  gases,  but  is  located  in  such  a  man- 
ner that  the  flow  of  the  flue  gases  over  the  superheating  surface 
may  be  controlled.  This  is  accomplished  by  installing  the  super- 
heater at  the  top  of  the  setting  near  the  side  of  the  steam  drum. 
The  superheater  is  enclosed  in  a  brick  setting  which  is  provided 
with  two  openings.  One  opening  is  near  the  rear  of  the  super- 
heater and  is  connected  to  the  furnace  gas  chamber  by  a  small 
brick  flue,  which  extends  downward  from  the  superheater  and 


62 


STEAM  AND  GAS  POWER  ENGINEERING 


terminates  near  the  bridge  wall.  The  other  opening,  which  is 
provided  with  a  damper,  is  near  the  front  of  the  superheater  and 
connects  with  the  flue  gases  as  they  pass  from  the  boiler.  The 
amount  of  superheat  can  be  regulated  by  varying  the  quantity 
of  gases  passing  over  the  superheating  surface.  The  superheater 
consists  of  a  number  of  U-shaped  tubes  connected  to  a  steel 
header.     The  header  is  divided  into  three  compartments. 

Foster  Superheater. — The  Foster 
superheater  makes  use  of  the  special 
tube  as  illustrated  in  Fig.  27.  The 
superheater  tubes  are  double  and  the 
outer  tubes  are  protected  by  cast  iron 
rings.  By  the  use  of  an  inner  and 
outer  tube,  the  steam  flows  against 
the  heated  surface  in  a  thin  stream, 
thus  increasing  the  effectiveness  of  the 
superheating  surface.  The  cast  iron 
rings  protect  the  outer  tube  from 
overheating,  so  that  no  flooding  is 
necessary. 

The  Foster  tubes  are  used  in  con- 
nection with  the  separately  fired  types 
as  well  as  with  the  attached  types  of 
superheaters. 

Mechanical  Stokers 


The  Field  of  Mechanical  Stokers. — 

Greatest  fuel  economy  can  be  secured 
by  firing  coal  frequently  and  in  small 
quantities.  With  hand  firing  this  is 
difficult  to  accomplish  and  usually 
more  coal  is  put  into  the  furnace  at 
one  time  than  is  desirable  for  eco- 
Mechanical    stokers    make  possible  the 


Fig. 


27. — Foster  superheater 
element. 


nomical  combustion, 
feeding  of*  small  quantities  of  fuel  at  regular  intervals,  the  time 
between  the  charges  being  so  regulated  that  the  fuel  is  completely 
burned.  When  using  mechanical  stokers  the  rate  of  firing  is 
even,  smoke  can  be  greatly  reduced,  the  furnace  doors  can  be  kept 


BOILER  AUXILIARIES  63 

closed,  and  the  air  supply  regulated  to  suit  the  fuel  and  the  load. 
Low  grade  fuels  which  cannot  be  burned  without  smoke  by  hand- 
firing  methods,  are  frequently  used  successfully  with  certain 
types  of  mechanical  stokers. 

Mechanical  stokers  are  an  absolute  necessity  in  large  power 
plants  on  account  of  the  saving  in  labor.  In  very  small 
plants,  stokers  are  not  often  used  on  account  of  the  initial  high 
cost  and  the  expenses  in  connection  with  the  operation  and 
upkeep  of  the  stoker  mechanism.  Stokers  are  practical  in 
plants  as  small  as  500-boiler  horsepower,  if  inferior  grades  of 
fuel  must  be  used,  the  skill  of  the  firemen  is  low,  or  smoke  must 
be  kept  down  to  a  minimum. 

The  cost  of  upkeep  is  higher  for  stokers  than  for  hand-fired 
furnaces,  and  is  influenced  by  the  size  and  by  the  composition  of 
the  fuel  used.  For  best  results  lumps  three  inches  or  smaller 
should  be  used.  The  initial  cost  of  stoker  equipment  depends 
upon  the  size  and  number  of  stokers  installed,  the  draft  available, 
and  the  kind  of  fuel. 

Mechanical  stokers  are  usually  classified  into  three  general 
types:  the  chain-grate,  the  inclined  grate,  and  the  underfeed 
type.  The  type  of  stoker  to  be  selected  depends  upon  the  kind 
of  fuel  to  be  burned. 

Chain-grate  Stokers. — Fig.  28  illustrates  a  typical  chain- 
grate  stoker.  The  entire  grate  surface  is  made  of  a  large 
number  of  chain-links,  which  form  the  fuel  bearing  surface. 
Sagging  of  the  upper  grate  surface  is  prevented  by  supporting 
the  weight  of  the  upper  grate  on  small  rollers. 

Power  for  driving  the  stoker  is  applied  at  the  front.  This 
causes  the  top  side  of  the  grate  to  revolve  slowly  from  the  front 
of  the  furnace  toward  the  rear.  Coal  is  fed  upon  the  moving 
grate  through  the  hopper  in  the  front  and  is  burned  as  it  passes 
toward  the  bridge-wall.  Under  proper  operating  conditions, 
the  speed  of  the  traveling  grate  is  adjusted  so  that  the  coal  will 
have  been  completely  burned  to  ash  when  it  reaches  the  end  of 
the  grate  and  will  drop  down  into  the  ash  pit  below.  The  speed 
of  the  chain  grate  must  be  regulated  in  accordance  with  the  load 
on  the  boiler  and  the  grade  of  coal  used.  Care  must  be  taken  in 
regulating  the  speed  of  the  grate  to  prevent  loss  of  fuel  to  the 
ashpit.     Leakage  of  air  between  the  grate  and  the  bridge  wall 


64 


STEAM  AND  GAS  POWER  ENGINEERING 


and  through  the  fire  bed  at  the  rear  must  be  reduced  to  a  mini- 
mum by  regulating  the  depth  of  the  fuel  and  ash  beds. 

This  type  of  stoker  is  usually  operated  with  natural  draft. 
The  entire  grate  is  mounted  upon  wheels  so  that  it  can  be  re- 
moved from  the  furnace  for  the  purpose  of  making  repairs.  A 
coking  arch  of  fire  brick  extends  over  the  top  of  the  grate  and 
acts  as  an  incandescent  surface  upon  which  the  volatile  gases 
strike  as  they  are  distilled  from  the  coal.  This  promotes  the 
complete  combustion  of  the  gases,  which,  if  allowed  to  strike 


Fig.  28. — Chain-grate  stoker. 

the  cooler  boiler  surface,  would  be  cooled  below  their  ignition 
temperature  and  smoke  would  result. 

The  chain-grate  stoker  is  best  suited  for  small  sizes  of  free 
burning,  non-caking,  and  high  ash  bituminous  coals.  This  type 
of  stoker  is  not  very  satisfactory  with  high-coking,  low  ash 
coals  on  account  of  the  fusing  action  of  the  fuel  under  the  fire 
brick  arch. 

Inclined  Grate  Stokers. — The  Roney  stoker,  illustrated  in 
Fig.  29,  is  representative  of  the  inclined  grate  over-feed  type. 
It  consists  of  a  hopper  for  receiving  the  coal,  a  series  of  stepped 
inclined  grate  bars,  which  extend  across  the  furnace,  and  a  dump- 


BOILER  AUXILIARIES 


65 


ing  grate  for  receiving  the  ash  and  clinkers.  The  grate  bars  are 
T-shaped  in  section  and  are  pivoted  near  their  lower  ends.  The 
lower  ends  of  the  stepped  bars  rest  in  slots  cut  in  the  rocker  bar. 
The  rocker  bar  is  given  a  reciprocating  motion  by  a  shaft  which 
passes  in  front  of  the  stoker  and  which  in  turn  receives  its  motion 
from  the  small  steam  engine.  The  coal  from  the  hopper  at  the 
front  of  the  stoker  first  strikes  a  dead  plate,  from  which  it  is 
pushed  on  to  the  inclined  grate  bars.  The  grate  bars  oscillate, 
alternately  assuming  a  horizontal  and  an  inclined  position,  thus 


Sectional  Throat  Piece 
(Always  specify 

of  pieces  wanted  > 
Hopper- En  d- 


boiler  Front  yT 


Stoker  Number 
Here  • 
Hopper  Shaft , 
Hand  Wheel ,  " 

Stud- 
Hand  Wheel  - 
Agitator  SectorJ 

Agitator-^ 
Sheath-Nut" 

Sheath'' 
Face-Nut  - 
Lock-Nut- 
£ccentric' 
Eccentric  Strap 
Damping  Grate  Handle' 
Connecting  Kod 
Guard  Handle 
Guard  Handle  Catch' 
Door  Handle 


Fig.  29. — Roney  stoker. 

slowly  sliding  the  coal  down  the  grate.  As  in  the  case  of  the 
chain-grate  stoker,  the  rate  of  feed  can  be  regulated,  and  when 
properly  operated  the  coal  should  be  completely  burned  when  it 
reaches  the  dumping  grate.  As  the  fuel  passes  under  the  fire 
brick  arch,  the  volatile  gases  are  mixed  with  heated  air,  the 
coal  is  coked,  and  smoke  is  greatly  reduced. 

The  Murphy  stoker,  illustrated  in  Fig.  30,  is  of  the  inclined 
grate,  side  feed,  type.  It  consists  of  a  Dutch  oven,  two 
coal  hoppers,  two  sets  of  inclined  grates,  and  a  stoking 
mechanism.     The  grate  bars  are  installed  so  that  only  alternate 

5 


66 


STEAM  AND  GAS  POWER  ENGINEERING 


ones  are  movable  and  these  are  given  a  motion  which  moves 
them  above  and  below  the  stationary  bars.  This  breaks  the 
adhesion  of  the  coal  to  the  bars  and  it  slowly  feeds  down  the 
inclined  grates.  A  toothed  clinker  bar  is  placed  in  the  bottom 
of  the  stoker  to  break  up  the  clinker. 


Transverse  Section 
Fig.  30. — Murphy  stoker. 


Underfeed  Stokers. — Fig.  31  illustrates  the  Jones  underfeed 
stoker.  It  consists  of  a  retort  placed  inside  the  furnace  and  of  an 
external  feeding  mechanism.  The  retort  is  trough-shaped  and 
along  each  side  are  placed  tuyere  blocks  for  admitting  the  air. 
The  feeding  mechanism  is  a  steam  cylinder  in  which  works  a 
piston.  A  coal  ram  is  attached  to  the  same  piston  rod. 
As  the  ram  forces  coal  into  the  retort,  the  coal  already  there  is 
forced  upward.  To  prevent  the  coal  from  heaping  up  near  the 
front  of  the  furnace,  pusher  blocks,  connected  to  the  piston  rod, 
are  placed  in  the  bottom  of  the  retort.  These  tend  to  maintain  a 
level  fire. 


BOILER  A  UXIL1 ARIES 


67 


The  operation  of  this  stoker  is  such  that  the  clinkers  and 
ash  are  worked  to  the  top  of  the  fire  and  are  removed  from  the 


31. — Jones  stoker, 


furnace  through  the  fire  doors  by  hand.  The  green  fuel  is  fed 
below  the  burning  coal,  and  the  hottest  part  of  the  furnace  is  at 
the  top  of  the  fuel  bed.     As  the  burning  coal  gradually  works  its 


Fig.  32. — Westinghouse  Stoker. 


way  toward  the  top,  any  volatile  matter  is  distilled  off  and  is 
consumed  before  reaching  the  furnace. 

Air  for  the  Jones  stoker  is  supplied  by  a  forced  draft  fan.     A 
duct  from  the  fan  leads  the  air  to  the  stoker  where  it  passes  into 


68         STEAM  AND  GAS  POWER  ENGINEERING 

the  furnace  through  the  tuyeres  in  the  retort.  This  class  of 
stoker  has  a  high  forcing  capacity  and  is  suitable  for  coking 
bituminous  coals. 

In  another  type  of  underfeed  stoker,  the  American,  the  piston 
is  replaced  by  a  worm,  which  continuously  feeds  the  coal  under- 
neath the  fire. 

Westinghouse  Stoker. — The  Westinghouse  stoker,  illustrated 
in  Fig.  32,  combines  the  principles  of  the  underfeed  and  of  the 
inclined  grate  types  of  stokers.  The  fuel  from  the  hopper  is  fed 
into  the  upper  retort,  which  is  located  in  the  bottom  of  the  coal 
hopper.  A  ram  in  the  retort  pushes  the  green  fuel  outward  and 
beneath  the  burning  fuel,  which  rests  upon  an  inclined  grate. 
The  green  fuel  being  introduced  under  the  fire  is  slowly  coked. 
The  lower  ram  forces  the  fuel  bed  and  refuse  toward  the  dump 
plates  at  the  rear.  The  stroke  of  the  lower  ram  can  be  regu- 
lated to  suit  the  load  and  the  fuel.  Air  for  the  combustion  of 
the  fuel  is  supplied  by  a  forced  draft  fan,  and  enters  the  fuel 
bed  through  openings  in  the  tuyere  boxes. 

Feed-water  Heaters  and  Economizers 

Feed-water  Heaters. — If  cold  water  is  fed  to  a  boiler,  there 
will  be  a  difference  in  temperature  at  the  various  parts  of  the 
boiler  shell,  and  strains  will  be  set  up  by  the  unequal  expansion 
and  contraction,  which  will  decrease  the  life  of  the  boiler,  be- 
sides impairing  the  tightness  of  the  setting.  With  hot  feed  water, 
strains  due  to  unequal  expansion  and  contraction  are  reduced. 
Modern  power  plants  are  usually  provided  with  feed-water  heaters, 
which  heat  the  water  by  exhaust  steam.  The  use  of  a  feed-water 
heater  will  increase  the  economy  of  a  steam  power  plant  by 
utilizing  exhaust  steam,  which  would  otherwise  be  wasted. 
Under  ordinary  conditions,  heating  feed  water  eleven  degrees 
will  produce  about  one  per  cent,  gain  in  economy.  The  capacity 
of  a  boiler  plant  can  be  increased  more  cheaply  by  the  installa- 
tion of  a  feed-water  heater,  outside  the  boiler,  than  by  increas- 
ing the  size  of  the  boiler.  Heating  the  feed  water  outside  of 
the  boiler  serves  also  to  purify  the  water  before  it  enters  the 
boiler. 

Feed  water  can  be  heated  by  live  steam,  by  exhaust  steam,  or 
by  the  waste  chimney  gases. 


BOILER  AUXILIARIES 


69 


The  heating  of  feed  water  by  live  steam  is  not  recommended, 
as  no  use  is  made  of  the  waste  heat. 

Feed-water  heaters  which  utilize  the  heat  of  exhaust  steam 
from  engines  and  pumps  are  most  commonly  used.  Heaters  may 
be  constructed  so  that  the  exhaust  steam  and  water  come  into 


Fig.  33. —  Open  feed  water  heater. 

direct  contact  and  the  steam  gives  up  its  heat  by  condensation. 
Such  heaters  are  called  open  feed-water  heaters.  One  type  of 
open  feed-water  heater  is  illustrated  in  Fig.  33.  In  this  form, 
water  passes  over  trays  upon  which  the  impurities  thrown  out 
of  the  water  by  the  heat  are  deposited,  and  can  be  easily  removed. 
Open  feed-water  heaters  are  provided  with  oil  separators  through 


70 


STEAM  AND  GAS  POWER  ENGINEERING 


Seamless 
Drawn 
Brass  - 


which  the  exhaust  steam  passes  before  entering  the  heater.  Open 
feed-water  heaters  are  usually  placed  on  the  suction  side  of  the 
feed  pump  and  at  a  higher  elevation  than  the  pump  cylinders  as  a 
feed  pump  cannot  lift  hot  water. 

If  it  is  desired  to  pass  the  water  through  the  heater  under  pres- 
sure or  to  prevent  the  steam  and  water  from  coming  into  contact 

with  each  other,  some  form 
of  closed  heater  should  be 
used.  Fig.  34  illustrates  a 
heater  of  this  type.  Here  the 
steam  on  one  side  of  the  tubes 
heats  the  water  on  the  other. 
Such  heaters  may  be  con- 
structed so  that  either  the 
steam  or  the  water  flows 
through  the  tubes.  Closed 
feed-water  heaters  are  more 
expensive  than  the  open 
types,  more  difficult  to  clean, 
and  are  used  only  in  special 
cases. 

Economizers. — A  feed- 
water  heater  which  derives  its 
heat  from  the  flue  gases  as 
they  leave  the  boiler  is  termed 
an  economizer.  Economizers 
increase  the  capacity  of  a 
boiler  plant  while  providing  a 
means  for  storing  large  quan- 
tities of  hot  water. 

Fig.  35  illustrates  an  econo- 
mizer connected  to  the  boiler. 
An  economizer  consists  of  a  series  of  straight,  vertical,  cast  iron 
tubes  connected  at  their  top  and  bottom  by  headers.  The 
boiler  feed  water  enters  at  the  end  nearest  the  chimney,  passes 
through  the  sections  of  tubes  and  is  heated  by  the  hot  gases 
that  circulate  through  them. 

The  economizer  is  usually  installed  in  such  a  manner  that  the 
gases  may  be  by-passed  around  the  tubes  or  through  them.     This 


'Exhaust 


Mud  Blow  S       Settling  Chamber 
Fig.  34. — Closed  feed  water  heater. 


BOILER  AUXILIARIES 


71 


provision  is  made  to  facilitate  repairs  without  shutting  down  the 
boiler. 

The  tubes  of  an  economizer  must  be  regularly  cleaned  both 
internally  and  externally.  The  heating  of  the  water  within  the 
tubes  causes  impurities  to  be  deposited,  which,  if  allowed  to 
accumulate,  would  impair  the  efficiency  of  the  tubes.  Handholes 
are  placed  over  each  tube  to  facilitate  the  cleaning  of  the  internal 
surface.     The  external  surface  of  the  tubes  must  be  freed  from 


Fig.  35. — Economizer. 


soot  and  moisture,  which  are  deposited  from  the  furnace  gases. 
The  cleaning  of  the  external  surface  of  the  tubes  is  accomplished 
by  a  mechanical  cleaner.  Small  cast  iron  scrapers  surround  each 
tube  and  are  made  to  slowly  travel  the  length  of  the  tube.  In 
this  manner,  any  soot  deposit  which  collects  upon  the  surface 
of  the  tube  may  be  removed. 

It  is  not  considered  good  practice  to  have  the  temperature  of 
the  water  entering  the  economizer  less  than  100°F.  Low  water 
temperatures  at  the  inlet  to  the  economizer  produce  sweating  of 


72         STEAM  AND  GAS  POWER  ENGINEERING 

the  first  rows  of  tubes,  and  may  result  in  the  corrosion  of  the 
economizer  tubes. 

An  economizer,  besides  providing  a  large  storage  of  hot  water 
for  sudden  demands,  increases  the  economy  of  a  steam  power 
plant  by  utilizing  the  heat  in  the  flue  gases.  The  reduction  of 
the  flue  gas  temperature,  due  to  the  absorption  of  heat  by  the 
economizer,  may  necessitate  the  addition  of  mechanical  draft 
apparatus,  or  an  increase  in  the  height  of  the  chimney.  The 
purity  of  the  feed  water,  the  sulphur  content  in  the  coal,  and  the 
cost  of  producing  additional  draft  should  be  considered  in 
connection  with  the  installation  of  economizers.  With  impure 
feed  water,  the  cost  of  keeping  the  economizer  tubes  clean  may 
be  excessive. 

Draft  Producing  Equipment 

Chimneys. — A  chimney  or  stack  is  used  to  carry  off  the  obnox- 
ious gases  formed  during  the  process  of  combustion,  to  discharge 
them  at  such  an  elevation  as  will  render  the  gases  unobjection- 
able, and  to  create  sufficient  draft  to  cause  fresh  air,  carrying 
oxygen,  to  pass  through  the  fuel  bed,  producing  continuous 
combustion.  The  majority  of  power  plants  depend  upon  chim- 
neys for  draft. 

The  draft  produced  by  a  chimney  is  due  to  the  fact  that  the  hot 
gases  inside  the  chimney  are  lighter  than  the  outside  cold  air. 
In  the  boiler  plant,  the  cold  air  is  heated  in  passing  through  the 
fuel  bed,  rises  through  the  chimney,  and  is  replaced  by  cold  air 
entering  under  the  grate.  This  means  that  the  amount  of  draft 
produced  by  a  chimney  depends  upon  the  flue  gas  temperature. 

The  intensity  of  the  draft  produced  by  a  chimney  depends  also 
on  its  height;  the  taller  the  chimney,  the  greater  is  the  draft 
produced,  since  the  difference  in  weight  between  the  column  of 
the  air  inside  and  that  of  the  air  outside  increases  as  the  height 
of  the  chimney. 

The  intensity  of  chimney  draft  is  measured  in  inches  of  water, 
which  means  that  the  draft  is  strong  enough  to  support  a  column 
of  water  of  the  height  given.  The  draft  produced  by  chimneys 
is  usually  one-half  to  three-fourths  of  an  inch  of  water. 

Chimneys  are  made  of  steel,  brick,  or  reinforced  concrete. 
For  small  plants  steel  stacks  are  most  desirable  on  account  of 


BOILER  AUXILIARIES 


73 


lower  first  cost  and  ease  of  construction  and  erection.     Self- 
sustaining  steel  stacks  are  used  in  some  large  power  plants 
on  account  of  the  smaller  space  required  as  compared  with  other 
stacks.     Steel   stacks  will    rust    and 
corrode    unless    they    are  kept   well 
painted. 

Brick  is  most  commonly  used 
where  permanent  chimneys  are  de- 
sired. A  brick  chimney,  unless  care- 
fully constructed,  will  allow  large 
quantities  of  air  to  leak  in,  which  will 
interfere  with  the  intensity  of  the 
draft.  Brick  chimneys  are  built 
round,  octagonal,  or  square,  and  are 
usually  constructed  with  two  walls 
and  an  air  space  between  them. 
The  inside  wall  is  lined  with  fire- 
brick. In  some  cases  chimneys  are 
built  of  hard  burned  brick  and  without 
lining.  The  thickness  of  the  chimney 
wall  decreases  by  a  series  of  steps,  as 
illustrated  in  Fig.  36. 

The  use  of  concrete  chimneys, 
reinforced  with  steel  rods,  is  increas- 
ing on  account  of  the  absence  of 
joints,  light  weight,  and  space  eco- 
nomy as  compared  with  brick  chim- 
neys. Ordinarily  a  reinforced  con- 
crete chimney  is  less  expensive  to 
build  than  a  brick  chimney. 

Draft  produced  by  chimneys  is 
called  natural  draft,  and  varies  as  the 
square  root  of  the  height.  The  ap- 
proximate boiler  horse-power  a  chim- 
ney will  serve  can  be  determined  by 
the  following  formula,  in  which  A  is 
the  internal  sectional  area  of  the  chimney  in  square  feet,  and  H  is 
its  height  above  the  grate  in  feet : 

Boiler  Horsepower  =  3.33  (A  -  0.6\/A)  Via- 


Fio.  36. — Brick  chimmey. 


74 


STEAM  AND  GAS  POWER  ENGINEERING 


Artificial  Draft. — In  large  power  plants  equipped  with  me- 
chanical stokers  or  economizers,  the  draft  produced  by  chimneys 
is  insufficient  and  some  artificial  method  has  to  be  used.  A  chim- 
ney once  built  is  limited  in  capacity  and  will  seldom  be  capable 
of  producing  a  draft  greater  than  0.75  inches  of  water,  or  about 
0.43  ounces  pressure.  Draft  produced  by  a  fan  may  have  a 
large  range  of  pressures,  depending  upon  the  speed  at  which  it  is 
operated. 

Artificial  draft  may  be  produced  by  steam  jets.  In  some  cases 
the  jets  discharge  beneath  the  grates,  forcing  the  air  and  steam 


Fig.  37. — Forced-draft  system. 

up  through  the  fuel  bed.  In  locomotives  the  jets  of  steam  from 
the  engine  exhaust  are  directed  upward  from  the  base  of  the 
stack.  Steam  jets  beneath  the  grates  are  cheap  to  install  and 
with  certain  varieties  of  coal  are  absolutely  necessary  in  order  to 
prevent  the  formation  of  clinkers.  Steam  jets  are  uneconomical, 
and  in  stationary  practice  preference  is  given  to  the  fan  or  the 
blower  systems  of  artificial  draft. 

The  method  by  which  the  fan  produces  draft  gives  rise  to  the 
forced  and  induced  draft  systems. 

In  the  forced  system,  Fig.  37,  the  air  delivered  to  the  furnace  is 
usually  taken  from  the  boiler  room,  and  a  duct  from  the  fan  dis- 
charges it  into  the  ash  pit.     The  air  is  thus  forced  into  the  fur- 


BOILER  AUXILIARIES 


75 


nace,  which  is  under  a  slight  pressure.  The  fact  that  the  pres- 
sure within  the  furnace  is  greater  than  that  of  the  atmosphere  is 
one  of  the  objections  to  the  forced  draft  system.  It  may  cause 
the  gas  to  leak  into  the  boiler  room  through  the  cracks  in  the 
setting,  and  the  flames  from  the  furnace  to  flare  out  when  the  fire 
doors  are  opened.     To  overcome  this  latter  objection,  the  system 


Induced-draft  system. 


must  be  equipped  with  suitable  dampers  for  shutting  off  the  air 
when  the  furnace  doors  are  opened. 

The  forced  draft  system  lends  itself  well  to  old  plants,  when 
the  draft  produced  by  chimneys  becomes  insufficient  on  account 
of  increased  demands  for  power.  The  forced  draft  system  is  also 
used  in  connection  with  the  underfeed  types  of  stokers. 

In  the  induced  draft  system,  Fig.  38,  the  suction  side  of  the  fan 


76         STEAM  AND  GAS  POWER  ENGINEERING 

is  connected  with  the  breeching  of  the  boiler,  and  the  products 
of  combustion  are  discharged  through  a  short  chimney.  The 
breeching  is  usually  provided  with  a  by-pass  direct  to  the  stack 
to  be  used  in  case  of  accident  to  the  fan.  The  furnace  and  ash 
pit,  in  the  case  of  the  induced  draft  system,  are  under  a  slight 
vacuum,  any  tendency  for  air  leakage  being  inward. 

Since  the  induced  draft  fan  handles  gases  at  temperatures  of 
400  to  500  degrees  F.,  it  must  be  much  larger  than  a  forced  draft 
fan  delivering  cold  air.  This  means  that  the  cost  of  the  induced 
draft  system  is  greater  than  that  of  the  forced  draft  system  for 
the  same  size  power  plant. 

The  induced  draft  system  is  generally  installed  with  economi- 
zers and  is  also  used  extensively  in  large  steam-electric  power 
plants  which  have  high  peak  loads. 

Mechanical  draft  permits  a  higher  rate  of  combustion  with 
less  air  per  pound  of  fuel  than  is  possible  with  natural  draft 
produced  by  chimneys.  A  forced  draft  system  for  a  large  power 
plant  will  cost  about  one-third  that  of  a  brick  chimney.  In- 
duced draft  system  will  cost  from  40  to  60  per  cent,  less  than  a 
brick  chimney.  To  offset  the  above  advantages  is  the  cost  of 
operating  the  mechanical  draft  system.  The  power  required 
to  operate  a  fan  will  amount  to  from  2  to  5  per  cent,  of  the  total 
boiler  steaming  capacity.  The  mechanical  draft  systems  have 
also  greater  depreciation  and  maintenance  costs  than  well  con- 
structed chimneys. 

Feed  Pumps  and  Injectors 

Water  is  forced  into  steam  boilers  by  pumps  or  injectors.  A 
pump  will  handle  water  at  any  temperature,  while  an  injector 
can  be  used  only  when  the  water  is  cold.  The  injector  is  not  as 
wasteful  of  steam  as  a  pump  and  for  feeding  cold  water  has  the 
additional  advantage  that  it  heats  the  water  while  feeding  it  to 
the  boiler. 

Feed  Pumps. — Feed  pumps  may  be  driven  from  the  cross-head 
of  an  engine.  Such  pumps  are  very  simple,  but  can  only  supply 
water  to  the  boiler  when  the  engine  is  in  operation. 

Direct  acting  steam  pumps,  driven  by  their  own  steam  cylin- 
ders, are  most  commonly  used  for  feeding  stationary  boilers,  as 
they  can  be  operated  independently  of  the  main  engine  and  their 


BOILER  AUXILIARIES 


77 


speed  can  be  regulated  to  suit  the  feed  water  demand  of  the  boil- 
ers. With  a  tight  suction  pipe  a  direct-acting  pump  will  lift 
cold  water  about   15  feet.     Centrifugal  pumps  are  frequently 


Fig.  39. —  Boiler  feed  pumps. 

used  in  large  power  plants  and  are  generally  driven  by  steam 
turbines. 

The  details  of  construction  of  two  forms  of  direct-acting  pumps 


78 


STEAM  AND  GAS  POWER  ENGINEERING 


are  shown  in  Fig.  39.  The  essential  difference  between  these 
pumps  is  that  one  uses  a  piston  and  the  other  a  plunger.  Both 
types  are  extensively  used.  The  piston  pattern  occupies  less 
floor  space,  but  is  more  difficult  to  pack. 

In  the  pump  shown  in  Fig.  39,  1  is  the  steam  cylinder  and  2  is 
the  water  cylinder.  The  valve  E  is  moved  by  the  vibrating  arm 
F,  and  admits  steam  into  the  cylinder,  1.  If  steam  is  admitted 
at  the  left  of  the  piston  A,  the  piston  will  be  moved  to  the  right, 


Fig.  40. — Boiler  feed  pump. 


pushing  the  plunger  B,  driving  the  water  through  the  valve  K} 
and  into  the  feed  line  at  0.  While  the  plunger  is  moving  to  the 
right,  a  partial  vacuum  is  formed  at  its  left  which  action  opens 
the  valve  N  and  draws  the  water  from  the  supply  at  C.  When 
the  plunger  B  reaches  the  extreme  position  to  the  right,  the  vibrat- 
ing arm  F  moves  the  valve  E  to  the  left,  admitting  steam  which 
pushes  the  piston  and  plunger  to  the  left,  driving  the  water 
through  the  valve  L  and  taking  a  new  supply  through  M .  The 
function  of  the  air  chamber  P  is  to  secure  a  steady  flow  of  water 


BOILER  AUXILIARIES 


79 


through  the  discharge  and  to  prevent  excessive  pounding  at 
high  speeds  by  providing  a  cushion  for  the  water. 

The  pump  shown  in  Fig.  40  differs  from  the  one  just  described 
in  that  the  steam  valve  G  is  operated  by  the  steam  in  the  steam 
chest  and  not  by  a  vibrating  arm  outside  of  the  cylinder.  The 
piston  C  is  driven  by  steam  admitted  under  the  slide  valve  G, 
this  valve  being  moved  by  a  plunger  F.  This  plunger  F  is 
hollow  at  the  ends  and  the  space  between  it  and  the  head  of  the 
steam  chest  is  filled  with  steam.  Thus  the  plunger  remains 
motionless  until  the  piston  C  strikes  one  of  the  valves  I,  exhausting 
the  steam  through  the  port  E  at  one  end.  The  water  end  is 
similar  to  that  of  the  pump  in  Fig.  39. 

Injectors. — Injectors  are  used  very  commonly  for  the  feeding 
of  locomotive,  portable,  and  small  stationary  boilers.  In  some 
power  plants  injectors  are  used  in  conjunction  with  pumps  as  an 
auxiliary  method  of  feeding  boilers. 


Steam 


Fig.  41. — Injector. 


The  general  construction  of  an  injector  is  illustrated  in  Fig. 
41.  Steam  from  the  boiler  enters  the  injector  nozzle  at  A, 
flows  through  the  combining  tube  BC,  and  out  to  the  atmosphere 
through  the  check  valve  E  and  overflow.  The  steam  in 
expanding  through  the  nozzle  A  attains  considerable  velocity, 
and  forms  sufficient  vacuum  to  cause  the  water  to  rise  to  the 
injector.  The  steam  jet  at  a  high  velocity  coming  into  contact 
with  the  water  is  condensed,  gives  up  its  heat  to  the  water,  and 
imparts  a  momentum  which  is  great  enough  to  force  the  water 


80 


STEAM  AND  GAS  POWER  ENGINEERING 


into  the  boiler  against  a  steam  pressure  equal  to  or  greater 
than  that  of  the  steam  entering  the  injector. 

As  soon  as  a  vacuum  is  established  in  the  injector  and  the  water 
begins  to  be  delivered  to  the  boiler,  the  check  valve  E  at  the  over- 
flow closes.  Should  the  flow  of  feed  water  to  the  boiler  be  inter- 
rupted, due  to  air  leaking  into  the  injector  or  to  some  other  cause, 
the  overflow  will  open  and  the  steam  will  escape  to  the  atmos- 
phere. 

Due  to  the  fact  that  the  vacuum  in  an  injector  is  broken  as 
the  temperature  of  the  water  increases,  injectors  can  work  only 
when  the  feed  water  is  150°F.  or  cooler. 

Duty  of  Pumps. — The  duty  of  a  pump  is  measured  in  foot 
pounds  of  work  done  in  moving  water  for  each  1,000  pounds  of 
steam  used,  or  for  each  million  British  thermal  units  delivered  in 
the  steam. 
Duty  per  million  B.t.u.  is: 

Water  horsepower  X  1,980,000  X  1,000,000. 
B.t.u.  in  steam  used  per  hour 

Small  direct-acting  pumps  have  duties  as  low  as  15,000  foot 
pounds  per  1,000  pounds  of  steam  used.  Large  pumping  engines 
have  shown  results  as  high  as  181,000,000  foot  pounds  per  1,000 
pounds  of  steam. 

Grates  for  Boiler  Furnaces 

Grates  are  formed  of  cast  iron  bars.  Several  forms  of  grate 
bars  are  illustrated  in  Figs.  42  and  43.     Plain  grates  (6),  Fig. 


Fig.  42. — Grate  bars. 


42,  are  best  adapted  for  caking  coals  and  are  usually  provided 
with  iron  bars,  cast  in  pairs,  and  with  lugs  at  the  side.  The 
Tupper  type  of  grate  (c)  Fig.  42,  is  more  suitable  for  the  burning 
of  hard  coal,  which  does  not  cake.     The  grates  of  a  boiler  furnace 


BOILER  AUXILIARIES  81 

can  be  easily  inter-changed  to  suit  the  fuel  burned.  For  most 
economical  results  some  form  of  rocking  and  dumping  grate,  as 
shown  in  Fig.  43,  should  be  used. 


Fig.  43. — Dumping  grate. 

Coal  and  Ash  Handling  Systems 

In  small  power  plants  the  coal  is  delivered  to  the  furnace  and 
the  refuse  is  removed  from  the  ash  pit  by  hand  shoveling.  In 
such  cases  the  coal  pockets  or  coal  bunkers  should  be  located 
opposite  the  boilers,  so  that  the  rehandling  of  coal  is  reduced  to 
a  minimum.  If  the  coal  cannot  be  stored  in  front  of  the  boilers, 
coal  tip-carts  are  found  very  satisfactory  for  conveying  the  fuel 
to  the  boiler  room. 

As  plants  increase  in  size,  mechanical  coal  and  ash  handling 
systems  are  warranted.  The  coal  handling  system  usually 
consists  of  the  following  equipment:  a  receiving  hopper,  into 
which  the  coal  is  delivered;  a  crusher,  which  reduces  the  fuel  to 
such  a  size  as  can  conveniently  be  handled  by  stokers;  elevating 
and  conveying  systems  for  raising  the  coal  from  the  crusher 
and  for  distributing  it  to  the  bunkers,  which  are  placed  over  the 
boilers;  and  spouts  which  deliver  the  fuel  from  the  bunkers  to  the 
stokers. 

The  endless  chain  bucket  conveyor  is  frequently  used  for 
handling  both  coal  and  ashes.  This  system  consists  of  a  con- 
tinuous series  of  buckets  suspended  between  two  endless  chains. 
The  discharge  of  the  coal  from  the  buckets  into  the  bunkers  over 
the  boilers  is  effected  by  a  tripping  device  which  turns  the  buckets 
over.  The  buckets  pass  beneath  ash  hoppers  under  the  boilers. 
The  ashes  are  elevated  by  the  buckets  and  discharged  into  an 
ash  storage  bin.  Hoist  and  trolley  systems,  scraper  conveyors, 
screw  conveyors,  and  belt  conveyors  are  also  used  in  handling 


82         STEAM  AND  GAS  POWER  ENGINEERING 

coal  and  ashes.  Vacuum  or  steam  conveyors  are  used  for  han- 
dling ashes  and  fine  coal.  Vacuum  and  steam  conveying  systems 
consist  of  a  pipe  line  through  which  the  ashes  or  fine  coal  are 
carried  by  air  or  steam  at  high  velocity. 

Problems 

1.  Discuss  the  advantages  of  superheaters  for  large  power  plants. 

2.  Report  on  the  uses  of  mechanical  stokers  in  the  power  plants  in  your 
vicinity. 

3.  Give  complete  directions  for  the  handling  of  an  underfeed  mechanical 
stoker. 

4.  Calculate  the  per  cent,  gain  which  will  result  from  preheating  feed  water 
to  200° F.,  from  a  temperature  of  70°F.,  if  a  boiler  plant  is  operated  at  a 
steam  pressure  of  140  pound  gage. 

5.  Examine  the  draft  producing  systems  in  the  power  plants  in  your  vicin- 
ity, and  hand  in  a  complete  report,  showing  types  of  stacks,  mechanical 
draft  systems,  and  the  intensity  of  the  draft  used. 

6.  A  pumping  engine  pumps  8,000,000  gallon  of  water  per  day  of  twenty- 
four  hours,  against  a  head  of  110  feet.  It  uses  2,500  pounds  of  steam  per 
hour.  If  the  steam  pressure  is  140  pounds  per  square  inch  gage,  and  the 
feed  water  temperature  is  202°F.,  calculate  the  duty  of  the  pumping  engine 
per  million  B.t.u. 


CHAPTER  VI 
PIPING  AND  BOILER  ROOM  ACCESSORIES 

Grades  and  Sizes  of  Piping. — Piping  used  to  convey  the  steam 
generated  in  a  boiler  is  made  of  wrought  iron  or  of  mild  steel. 
Wrought  iron  pipe  is  superior  to  steel  pipe,  as  it  is  softer,  is 
easier  to  thread,  and  is  not  subject  to  corrosion.  Wrought 
iron  pipe  is  more  expensive  and  more  difficult  to  secure  than 
steel  pipe.  The  largest  portion  of  piping  used  in  power  plants  is 
of  mild  steel,  lap  or  butt  welded  for  high  pressures.  Cast  steel 
pipe  has  been  found  more  suitable  for  superheated  steam  than 
mild  steel  pipe. 

Sizes  of  standard  steam  pipe  up  to  12  inches  are  named  by 
their  inside  diameter;  above  12  inches  they  are  designated 
by  their  outside  diameter.  The  sizes  of  boiler  tubes  are  given  by 
their  outside  diameter. 

Standard  steam  pipe  is  made  in  sizes  of  }i,  }>i,  %,  %,  Y±,  1, 
1H,  IK,  2,  2K,  3,  3}i,  4,  4^,  5,  6,  7,  8,  9,  10,  11,  and  12  inches. 
Standard  pipe  is  suitable  for  pressures  up  to  125  pounds  per 
square  inch. 

The  various  grades  of  pipe  are:  standard,  extra  heavy,  and 
double  extra  heavy.  Extra  heavy  and  double  extra  heavy  have 
the  same  outside  diameter  as  standard  pipe,  but  the  inside 
diameters  are  smaller,  due  to  the  greater  thickness  of  the  pipe. 
Extra  heavy  pipe  is  suitable  for  pressures  up  to  250  pounds  per 
square  inch,  while  double  extra  heavy  pipe  can  be  used  for 
pressures  up  to  about  1,000  pounds  per  square  inch. 

Pipe  Fittings. — Two  kinds  of  fittings  are  used  in  steam  power 
plants,  the  screwed  and  the  flanged  fittings.  For  saturated  steam 
and  for  pressures  less  than  150  pounds,  all  fittings  3  3^  inches  and 
under  may  be  screwed.  Fittings  4  inches  and  over  should  have 
flanged  ends.  Screwed  fittings,  when  properly  installed,  are 
less  liable  to  leak  than  flanged  fittings,  which  are  put  together 
with  gaskets.  Flanged  fittings  are  easily  taken  apart  and  are 
most  generally  used  in  modern  power  plants. 

83 


84  STEAM  AND  GAS  POWER  ENGINEERING 

The  pipe  fittings  most  commonly  used  are  illustrated  in  Figs. 
44  to  52. 


Fig.  44. — Pipe  unions  and  couplings. 


Fig.  45.— Ells. 


Fig.  46.— Reducing  ell.  Fig.  47. — Tees. 


Fig.  48.— Cross.     Fig.  49.— Bush-     Fig.  5  0.  —  Re- 


ing. 


ducer. 


Fig.  51. — Cap.  Fig.  52. — Plug. 

Fig.  44  illustrates  several  forms  of  pipe  unions  and  couplings, 
which  are  used  for  uniting  two  lengths  of  pipe. 


PIPING  AND  BOILER  ROOM  ACCESSORIES         85 


The  elbow  or  ell  shown  in  Fig.  45  is  employed  for  connecting 
two  pipes,  of  the  same  size,  at  an  angle  to  each  other.  If  the  pipes 
are  of  different  diameters  a  reducing  ell,  as  shown  in  Fig.  46, 
should  be  used. 

The  tee  shown  in  Fig.  47  is  used  for  making  a  branch  at  right 
angles  to  a  pipe  line. 

The  cross  shown  in  Fig.  48  is  used  when  two  branches  must  be 
connected  in  opposite  directions. 

In  order  to  reduce  the  size  of  a  pipe  line,  a  bushing,  Fig.  49, 
or  a  reducer,  Fig.  50,  can  be  used. 

To  close  the  end  of  a  pipe,  a  cap,  Fig.  51,  is  used,  while  the 
plug  shown  in  Fig.  52,  is  used  to  close  a  fitting  threaded  on  the 
inside. 

In  cast  iron  flanged  fittings  the  flange  is  always  a  part  of  the 
casting.  For  joining  two  ends  of  a  pipe,  the  pipe  and  flange 
are  threaded,  the  pipe  is  screwed  beyond  the  face  of  the  flange, 
and  the  two  are  faced  off  together.  Another  method  is  to  weld 
the  flanges  on  the  pipe. 

Expansion  of  Piping. — In  piping  systems,  provision  must  be 
made  to  allow  for  the  expansion  and  contraction  due  to  variation 

in  the  temperature  of  the  steam  within 
the  pipe.  Unless  a  pipe  expands  freely, 
distortion  or  injurious  strains  on  the 
joints  and  fittings  will  occur. 

The  simplest  method  is  to  permit  the 


Fig.    53. — Double-swing     ex- 
pansion joint. 


Fig.  54. — Long  radius  bends. 


expansion  to  adjust  itself  in  a  threaded  joint.  Such  an  arrange- 
ment is  shown  in  Fig.  53.  Any  expansion  or  contraction  in  the 
piping  is  adjusted  by  a  slight  movement  in  the  screwed  joints. 

Another  method  quite  extensively  used  in  high  pressure 
piping  is  to  insert  a  long  radius  bend,  as  illustrated  in  Fig.  54. 
A  long  radius  bend,  besides  taking  care  of  the  expansion  after 


86 


STEAM  AND  GAS  POWER  ENGINEERING 


the  piping  is  in  place,  reduces  the  number  of  joints,  decreases 
friction,  and  is  much  easier  to  erect  than  pipe  fittings.  One  of 
the  objections  against  the  use  of  long  radius  bends  is  the  space 
required. 

The  slip  expansion  joint  illustrated  in  Fig.  55  overcomes  the 
above  objection.  The  main  casting  of  this  expansion  joint  is 
divided  into  two  parts.  The  expansion  or  moving  element 
consists  of  a  non-corrodible  bronze  sleeve,  made  steam  tight 
by  the  long  stuffing  box.  The  sleeve  is  supported  at  the  outer 
end  by  flanges.  In  installing  a  slip  expansion  joint,  the  pipe 
must  be  securely  anchored  to  prevent  the  steam  pressure  from 
forcing  the  joint  apart. 


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Pipe  Covering. — All  pipes  carrying  steam  and  hot  water  should 
be  covered  with  some  heat  insulating  material  in  order  to  reduce 
the  loss  of  heat  to  a  minimum.  If  saturated  steam,  is  conveyed 
in  uncovered  steam  pipes,  some  of  it  will  condense,  reducing  the 
economy  of  the  plant.  Tests  demonstrate  that  pipe  covering 
will  pay  for  itself  in  a  very  short  time. 

Pipe  covering  is  usually  applied  in  sections,  molded  to  the  re- 
quired size  of  the  pipe  and  secured  to  the  pipe  by  bands.  Valves 
and  fittings  are  usually  covered  with  a  plastic  insulating  mortar. 

Erecting  Pipe. — Steam  pipe  lines  should  always  be  laid  with  a 
gradual  slope  in  the  direction  in  which  the  steam  flows.  This  will 
allow  the  condensation  and  the  steam  to  flow  in  the  same  direc- 
tion.    If  this  is  not  done  water  may  accumulate,  will  be  picked 


PIPING  AND  BOILER  ROOM  ACCESSORIES         87 

up  by  the  steam,  and  may  cause  much  damage  either  to  the  fit- 
tings or  to  the  engine. 

Care  must  be  taken  that  the  pipe  lines  have  the  proper  align- 
ment in  order  to  prevent  strain  on  the  fittings.  Pipe  lines  must 
be  supported  by  wall  brackets,  hangers,  or  floor  stands  to  guard 
against  excessive  deflection  and  vibration. 

Valves. — The  function  of  a  valve  is  to  control  and  regulate 
the  flow  of  water,  steam,  or  gas  in  a  pipe.  In  the  globe  valve, 
Fig.  56,  the  fluid  usually  enters  at  the  right,  passes  under  the 


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Fig.  57. — Gate  valve. 


valve,  and  out  at  the  left.  This  method  of  installation  permits 
the  valve  stem  to  be  packed,  when  the  valve  is  closed,  without 
cutting  the  steam  pressure  off  the  entire  line. 

If  a  globe  valve  is  installed  so  that  the  fluid  enters  at  the  left. 
Fig.  56,  the  pressure  of  the  steam,  when  the  valve  is  closed,  tends 
to  keep  it  in  that  position  and  there  is  much  less  likelihood  of  the 
valve  leaking,  but  the  valve  cannot  be  opened  if  it  should  be- 
come detached  from  the  stem. 

Globe  valves  in  sizes  up  to  three  inches  have  brass  bodies;  large 
valves  are  made  of  cast  iron  for  ordinary  pressures  and  tempera- 
tures, and  of  cast  steel  for  high  temperatures  and  pressures. 

A  gate  valve  is  shown  in  Fig.  57.  This  form  of  valve  gives  a 
straight  passage  through  the  valve,  and  is  preferable  for  most 
purposes  to  the  globe  valve.     For  high  pressure  work  and  in 


88 


STEAM  AND  GAS  POWER  ENGINEERING 


large  sizes,  gate  valves  are  usually  of  the  outside  screw  type,  which 
means  that  the  stem  protrudes  beyond  the  hand  wheel.  This 
enables  the  operator  to  tell  at  a  glance  whether  the  valve  is  open 
or  closed.  The  gate  valve  illustrated  in  Fig.  57  is  of  the  inside 
screw  type,  and  is  used  in  small  sizes  and  also  in  plants  where  the 
screw  must  be  protected  from  dirt. 

Fig.  58  illustrates  an  angle  valve  which  takes  the  place  of  an 
ordinary  valve  and  ell. 

The  function  of  a  check  valve,  illustrated  in  Fig.  59,  is  to  allow 
water  or  steam  to  pass  in  one  direction  but 
not  in  the  other.  A  boiler  feed  line  should 
always  be  provided  with  a  check  valve  and 
also  with  some  form  of  globe  or  gate  valve  to 
enable  the  operator  to  examine  and  repair  the 
check  valve. 


Fia.  58. — Angle  valve. 


Fig.  59. — Check  valve. 


Blow-off  Valves. — A  boiler  should  always  be  provided  with  a 
blow-off  connection  at  its  lowest  point  for  removing  mud  and 
sediment,  as  well  as  for  the  purpose  of  draining  the  boiler.  The 
blow-off  connections  must  be  provided  with  blow-off  valves, 
which  can  be  easily  opened,  which  will  give  a  free  passage  for  scale 
and  sediment  when  open,  and  which  will  not  leak  when  closed. 
Best  practice  recommends  the  use  of  two  valves  or  of  a  valve  and 
a  blow-off  cock  in  the  blow-off  line  of  each  boiler. 

Safety  Valves. — The  function  of  a  safety  valve  is  to  prevent 
the  steam  pressure  from  rising  to  a  dangerous  point.  The  two 
common  forms  of  safety  valves  are :  the  lever  safety  valve  and 
the  spring  or  pop  safety  valve. 

The  lever  safety  valve  shown  in  Fig.  60  consists  of  a  valve  disc 
which  is  held  down  on  the  valve  seat  by  means  of  a  weight  acting 
through  a  lever,  the  steam  pressing  against  the  bottom  of  the  disc. 


PIPING  AND  BOILER  ROOM  ACCESSORIES        89 

The  lever  is  pivoted  at  one  end  to  the  valve  casing,  and  is  marked 
at  a  number  of  points  with  the  pressures  at  which  the  boiler  will 
blow  off  if  the  weight  is  placed  at  that  particular  point.  Lever 
safety  valves  are  seldom  used  in  modern  power  plants. 


Fig.  60. — Lever  safety  valve. 


Fig.  61. — Pop  safety  valve. 


The  pop  safety  valve  shown  in  Fig.  61  differs  from  the  lever 
valve  in  that  the  valve  disc  is  held  on  its  seat  and  the  steam 
pressure  is  resisted  by  a  spring,  in  place  of  a  weight  and  levers 
Pop  safety  valves  can  be  adjusted  to  blow  off  at  various  pressure, 
by  tightening  or  loosening  the  spring  pressure  on  the  valve  disc. 


Fig.  62. — Steam  gages. 

The  American  Society  of  Mechanical  Engineers  recom- 
mends that  two  or  more  safety  valves  be  installed  on  every 
boiler,  except  in  the  case  of  small  boilers  which  require  a  safety 
valve  3  inches  or  smaller. 

Steam  Gages. — A  steam  gage  indicates  the  pressure  of  the 
steam  in  a  boiler.     The  most  common  form,  shown  in  Fig.  62, 


90 


STEAM  AND  GAS  POWER  ENGINEERING 


consists  of  a  curved  spring  tube  closed  at  one  end.  One  end  of 
the  tube  is  free,  while  the  other  is  fastened  to  the  fitting  which 
is  secured  into  the  space  where  the  pressure  is  to  be  measured. 
The  cross  section  of  the  tube  is  made  elliptical  or  irregular  in 
shape  so  that  pressure  applied  to  the  inside  of  the  tube  causes 
the  free  end  to  move.  This  motion  is  communicated  by  means 
of  levers  and  small  gears  to  the  needle  which  moves  over  a 
graduated  dial  face,  and  records  the  pressure  directly  in  pounds 
per  square  inch. 

Water  Glass  and  Gage  Cocks. — The  height  of  the  water  level 
in  a  boiler  is  indicated  by  a  water  glass,  one  end  of  which  is 
connected  to  the  steam  space  and  the  other  end  to  the  water 
space  in  the  boiler.     All  boilers  should  also  be  provided  with  three 

gage  cocks,  one  of  which  is  set  at  the 
desired  water  level,  one  above  it  and 
one  below.  These  are  more  reliable 
than  the  water  glass  and  should  be  used 
for  checking  the  glass. 

Water  Column. — The  steam  gage, 
water  glass,  and  gage  cocks  are  usually 
fastened  to  a  casting  called  a  water 
column.  One  form  of  water  column  is 
shown  in  Fig.  63.  This  water  column 
is  fitted  with  a  float  and  a  whistle  to 
notify  the  operator  should  the  water  in 
the  boiler  become  too  low  or  too  high. 
An  operator  who  takes  proper  care  of 
the  boilers  in  his  charge  will  never 
allow  the  water  to  be  at  a  height  that 
will  necessitate  audible  warnings. 
Steam  Traps. — The  object  of  a  steam 
trap  is  to  drain  the  water  from  pipe  lines  without  allowing  the 
steam  to  escape.  One  form  of  steam  trap  is  shown  in  Fig.  64; 
in  this  case  the  valve  is  controlled  by  a  float  when  the  water  in 
the  trap  rises  to  a  sufficient  height.  In  another  type  of  trap, 
called  the  bucket  type,  there  is  a  bucket  in  the  interior  of  the 
trap,  which  when  filled  with  the  condensed  steam  operates  as  a 
float  and  opens  a  valve. 


Water  column. 


PIPING  AND  BOILER  ROOM  ACCESSORIES        91 

Traps  which  receive  the  condensed  steam  and  return  it  to  the 
boiler  are  called  return  traps. 


Fig.  64. — Steam  trap. 

Fusible  Plugs. — Plugs  with  a  core  of  some  fusible  metal  are 
used  to  protect  boilers  from  overheating.  If  a  plate,  into  which 
a  fusible  plug  is  screwed,  becomes  overheated,  the  fusible  metal 
melts  and  runs  out  allowing  the  steam  and  hot  water  to  run  in- 
to the  boiler  furnace. 

Fusible  plugs  are  placed  about  three  inches  above  the  top  row 
of  tubes  in  a  cylindrical  tubular  boiler  and  in  the  lower  side  of 
the  upper  drum  of  a  water  tube  boiler. 


Problems 

1.  Make  a  clear  sketch  showing  the  location  of  the  boiler  stop  valve  with 
reference  to  the  piping  from  the  boiler. 

2.  Make  an  inspection  of  some  plant  in  your  vicinity  and  report  on  the 
following : 

(a)  Types  of  fittings  used. 

(6)  Are  the  steam  pipes  covered?     If  so,  with  what  material. 

3.  Make  a  clear  sketch  showing  how  you  would  arrange  the  piping  and 
fittings  in  connection  with  a  boiler  blow-off  connection. 

4.  Where  should  safety  valves  be  placed  on  fire  tube  boilers?     On  water 
tube  boilers? 

6.  Sketch  three  (3)  forms  of  pipe  supports. 

6.  Why  place  a  fusible  plug  about  three  inches  above  the  top  row  of  tubes 
in  a  cylindrical  tubular  boiler? 


CHAPTER  VII 
STEAM  ENGINES 

Description  of  the  Steam  Engine. — A  steam  engine  is  a  motor 
which  utilizes  the  energy  of  steam.  It  consists  essentially  of  a 
piston  and  cylinder  with  valves  to  admit  and  to  exhaust  the  steam, 
a  governor  for  regulating  the  speed,  some  lubricating  system  for 
reducing  friction,  and  stuffing  boxes  for  preventing  steam  leakage. 

In  the  steam  engine  working  as  a  motor,  continuous  rotary 
motion  of  the  shaft  is  essential.  This  is  accomplished  by  the  inter- 
position of  a  mechanism  consisting  of  a  connecting  rod  and  crank, 
which  changes  the  to-and-fro,  or  reciprocating  motion,  of  the 
piston  into  mechanical  rotation  at  the  shaft.  A  steam  engine  in 
which  the  reciprocating  motion  of  the  piston  is  changed  into 
rotary  motion  at  the  crank  is  called  a  reciprocating  steam  engine 
to  differentiate  it  from  the  steam  turbine  to  be  described  in  a 
later  chapter. 

The  various  parts  of  a  steam  engine  are  illustrated  in  Figs. 
65,  66  and  67. 

Steam  from  the  boiler  at  high  pressure  enters  the  steam  chest 
A,  Fig.  65,  and  is  admitted  alternately  through  the  ports  BB 
to  either  end  of  the  cylinder  by  the  valve  C.  The  same  valve  also 
releases  and  exhausts  the  steam  used  in  pushing  the  piston  D. 
E  is  the  cylinder  in  which  the  steam  is  expanded.  The  motion  of 
the  piston  D,  Fig.  66,  is  transmitted  through  the  piston  rod  F 
to  the  crosshead  G,  and  through  the  connecting  rod  H  to  the 
crank  I,  which  is  keyed  to  the  shaft  K. 

The  shaft  is  connected  directly,  or  by  means  of  intermediate 
connectors,  such  as  belts  or  chains,  to  the  machines  to  be  driven. 

The  shaft  carries  the  flywheel  L  (Fig.  66),  the  function  of  which 
is  to  make  the  rate  of  rotation  as  uniform  as  possible  and  to  carry 
the  engine  over  the  dead-centers.  The  dead-center  occurs  when 
the  crank  and  connecting  rod  are  in  a  straight  line  at  either  end  of 
the  stroke,  at  which  time  the  steam  acting  on  the  piston  will  not 

92 


STEAM  ENGINES 


93 


turn  the  crank.    A  flywheel  is  sometimes  used  as  a  driving  pulley, 
as  shown  in  Fig.  67. 

tC\\\\\\\-( ,  i  i   ,  i    i  i  ,1    i  i  1  1  11 


Fig.  65. — Engine  cylinder  and  steam  chest. 

The  eccentric  shown  in  Fig.  67  also  rotates  with  the  shaft,  and 
its  function  is  to  impart  a  reciprocating  motion  to  the  valve.  The 
eccentric  consists  of  a  circular  iron  disk,  so  keyed  to  the  shaft 


Fig.  66. — Steam  engine. 

that  its  center  is  eccentric  to  the  center  of  the  shaft.  Around 
the  eccentric  fits  a  ring,-  called  the  eccentric  strap.  The  eccen- 
tric strap  is  bolted  to  a  rod,  called  the  eccentric  rod.     The  eccen- 


94 


STEAM  AND  GAS  POWER  ENGINEERING 


trie  imparts  a  backward  and  forward  motion  to  the  valve  through 
the  eccentric  rod  and  valve  stem.  This  motion  given  to  the  valve 
is  dependent  upon  the  eccentricity  of  the  eccentric.  The  eccen- 
tricity is  the  distance  between  the  center  of  the  eccentric  and  the 
center  of  the  shaft.  Changing  the  eccentricity  changes  the  travel 
of  the  valve.  The  travel  of  the  valve,  or  the  total  distance  it  moves, 
is  equal  to  the  throw  of  the  eccentric,  or  to  twice  the  eccentricity. 


Top  Cylinder-^^i 
Heat,  ' 


Cylinder  ~>\ 
Lacjo/incf 


Bo-Hvm  Cylinder^ 
Head 


Cross- Head-   . 
Oiler  Bracket 


Valve  Stem  Driver 
Valve  Stem  Square 


Drivinq 
Pultef 


Fig.  67. — Vertical  steam  engine. 


Stuffing  boxes  which  prevent  the  escape  of  steam  around  the 
rods  are  illustrated  at  M  and  N  in  Figs.  65  and  66  respectively. 

Early  History  of  the  Steam  Engine. — The  use  of  steam  for  the 
pumping  of  water  dates  back  to  about  1700.  The  operation  of 
the  engines  of  that  time  differed  from  the  modern  steam  engine 
in  that  steam  was  admitted  into  a  closed  vessel,  at  atmospheric 
pressure,  and  was  condensed  by  throwing  cold  water  over  the 
external  surface  of  that  vessel.  The  vacuum  thus  created  was 
utilized  in  the  production  of  work. 


STEAM  ENGINES  95 

The  Newcomen  engine  of  1705  first  made  use  of  a  cylinder  and 
piston,  but  worked  on  the  same  principle  as  the  engines  mentioned 
above. 

In  1712  Newcomen  designed  a  steam  engine  in  which  the  con- 
densation of  the  steam  was  affected  by  introducing  water  into  the 
cylinder.  The  operation  of  the  valves  in  the  Newcomen  engine 
was  by  hand  and  steam  at  only  atmospheric  pressure  was  utilized. 

In  1718  Henry  Brighton  invented  a  self-acting  machine.  The 
valves  consisted  of  a  series  of  tappets  operated  by  the  beam 
of  the  engine. 

James  Watt  in  1769  laid  the  foundation  for  the  modern  steam 
engine.  His  greatest  improvements  consisted  in  transferring 
the  steam  to  another  vessel  for  condensation,  making  use  of  pres- 
sure greater  than  atmospheric,  constructing  the  steam  engine 
double-acting,  and  in  inventing  the  steam  engine  indicator. 
Watt  was  the  first  to  realize  the  advantages  resulting  from  using 
steam  expansively,  although  this  was  applied  to  an  actual  engine 
by  Wolfe  in  1804.      ■ 

Losses  in  Steam  Engines. — The  main  losses  in  a  steam  engine 
are: 

1.  Loss  in  pressure  as  the  steam  is  transferred  from  the  steam 
boiler  to  the  engine  cylinder,  due  to  the  throttling  action  in  the 
steam  pipe  and  ports.  Steam  in  passing  through  a  small  port  loses 
part  of  its  energy  in  overcoming  friction.  To  reduce  such  losses 
to  a  minimum,  the  pipes  and  ports  must  be  ample  and  all  steam 
passages  must  be  as  straight  as  possible. 

2.  Leakage  past  piston  and  valves.  The  losses  due  to  leakage 
past  the  piston  and  valves  are  usually  very  small  in  well  designed 
engines  and  may  be  kept  so  by  proper  attention.  . 

3.  Loss  due  to  the  condensation  of  the  steam  in  the  cylinder. 
This  loss  takes  place  when  the  entering  steam  comes  in  contact 
with  the  cylinder  walls,  which  have  been  cooled  by  the  exhaust 
steam  which  previously  filled  the  cylinder.  Cylinder  conden- 
sation becomes  greater  as  the  difference  between  the  admission 
and  exhaust  pressures  is  increased.  When  steam  is  sufficiently 
superheated,  no  condensation  takes  place,  but  the  loss,  though 
somewhat  lessened,  is  still  present. 

Losses  due  to  condensation  of  steam  within  the  cylinder  can 
also  be  decreased  by  increasing  the  engine  speed,  by  regulating 


96 


STEAM  AND  GAS  POWER  ENGINEERING 


the  point  of  cut-off,  by  compounding,  using  steam  jackets,  increas- 
ing the  size  of  the  units,  or  by  employing  the  uniflow  principle, 
to  be  described  later. 

4.  Radiation  losses.  Radiation  losses  take  place  when  the 
steam  passes  through  the  steam  pipes  from  the  boiler  to  the 
cylinder  and  also  while  the  steam  is  in  the  cylinder.  Radiation 
losses  in  the  steam  pipes  leading  from  the  boiler  to  the  engines 
can  be  reduced  by  the  use  of  a  good  pipe  covering.  The  radia- 
tion losses  from  the  cylinder  of  the  engine  are  reduced  by  jack- 
eting the  cylinder  with  some  non-conducting  material. 


Fig.  68.—  Engine  cylinder  and  plain  slide  valve. 

5.  Losses  of  heat  in  the  exhaust  steam.  Seventy-five  per 
cent,  or  more  .of  the  heat  available  in  the  steam  when  it  enters 
the  engine  cylinder  is  carried  away  in  the  exhaust.  Part  of  this 
heat  can  be  recovered  by  using  the  exhaust  steam  for  the  heating 
of  feed  water  before  it  enters  the  boiler,  for  the  heating  of  build- 
ings, or  in  employing  the  exhaust  steam  in  connection  with 
various  manufacturing  processes. 

6.  Mechanical  losses  due  to  the  friction  of  the  moving  parts. 
These  losses  may  be  kept  at  a  minimum  by  proper  lubrication. 

Action  of  the  Plain  Slide  Valve. — Fig.  68  shows  a  section 
through  a  steam  engine  cylinder  with  the  slide  valve  in  mid-posi- 
tion.    A  and  B  are  the  steam  ports,  which  lead  to  the  two  ends  of 


STEAM  ENGINES 


97 


the  cylinder;  C  is  the  exhaust  space.  The  steam  ports  are  sepa- 
rated from  the  exhaust  space  by  the  two  bridges,  D  and  E.  F  is 
the  steam  chest.  V  is  a  plain  slide  valve,  commonly  called  a  D 
slide  valve.  The  amount  S  that  the  valve  V  extends  over  the 
outside  edge  of  the  port,  when  the  valve  is  at  the  center  of  its 
travel,  is  called  the  steam  lap.  Similarly  the  amount  X  by  which 
the  valve  over  laps  the  inside  edge  of  the  port  when  it  is  in  mid- 
position  is  called  the  exhaust  lap.  M  and  N  are  the  steam  and 
exhaust  pipes  respectively. 

A  term  frequently  used  in  connection  with  the  operation  of 
valves  is  "lead."  By  lead  is  meant  the  amount  that  the  port  is 
uncovered  when  the  engine  is  on  either  dead-center.  The  object 
of  lead  is  to  supply  full  pressure  steam  to  the  piston  as  soon  as  it 
passes  the  dead-center. 


Fig.  69. — Admission. 


Fig.  70.— Cut-off. 


The  motion  of  the  valve  produces  four  events:  admission, 
cut-off,  release,  and  compression.  Admission  is  that  point  at 
which  the  valve  is  just  beginning  to  uncover  the  port.  The 
position  of  the  valve  for  this  event  is  shown  in  Fig.  69.  Cut- 
off occurs,  Fig.  70,  when  the  valve  covers  the  port,  preventing 


Fig.  71. — Release. 


Fig.  72. — Compression. 


further  admissioi)  of  steam.  This  is  followed  by  the  expansion 
of  the  steam  until  the  cylinder  is  communicated  with  the  exhaust 
opening,  at  which  time  release,  as  shown  by  Fig.  71,  occurs. 
Compression  occurs  when  communication  between  the  cylinder 
and  exhaust  opening  is  interrupted,  Fig.  72,  and  the  steam  remain- 
ing in  the  cylinder  is  slightly  compressed  by  the  piston.  The 
valve  is  in  the  same  position  at  cut-off  as  it  is  at  admission,  only 

7 


98         STEAM  AND  GAS  POWER  ENGINEERING 


y////////////c 


it  is  traveling  in  the  opposite  direction.     Similarly  the  positions 
of  the  valve  are  the  same  at  release  and  compression. 

Types  of  Plain  Slide  Valves. — If  the  valve  is  constructed 
without  laps,  as  shown  in  Fig.  73,  there  is  no  period  of  valve 
closure,  and  the  steam  acts  non-expansively.  The  release  and 
the  cut-off  of  the  steam  occur  at  practically  the  same  instant. 
The  steam  admission  in  one  end  of  the  cylinder  takes  place 
throughout  the  entire  stroke,  while  the  steam  in  the  opposite 
end  of  the  cylinder  is  exhausted  at  the  same  time.     Such  a  valve 

would  be  uneconomical  because  of  its 
failure  to  provide  for  the  expansion  of 
,       the  steam,  and  as  a  result  is  only  re- 
\       sorted    to   in  the    direct-acting   steam 

FiG.TS.-Valvewithoutlaps.    PumP'    which   is   essentially   a   special 

case.  For  best  economy  a  steam  engine 
should  be  provided  with  a  valve  which  cuts  off  the  steam  at 
about  one-third  of  the  stroke  and  releases  it  somewhere  near 
the  end  of  the  stroke. 

The  simplest  type  of  valve  for  steam  engines  is  the  plain  slide 
valve,  illustrated  in  Fig.  68.  This  type  of  valve  is  not  used  where 
steam  economy  has  to  be  considered.  The  plain  slide  valve  is  used 
to  a  limited  extent  in  connection  with  portable  engines,  traction 
engines,  or  small  stationary  steam  engines.  The  chief  ob  j  ection  to 
its  use  on  engines  of  larger  sizes  is  that  it  is  not  balanced.  If  the 
difference  between  the  steam  and  the  exhaust  pressures  is  large, 
the  force  of  the  steam  holding  the  valve  upon  its  seat  is  also 
large,  and  consequently  the  force  required  to  move  the  valve 
backward  and  forward  may  be  excessive.  This  consumes  a  part 
of  the  work  developed  by  the  engine,  needlessly  strains  the  valve- 
gear,  and  makes  it  difficult  to  keep  the  valve  steam-tight  The 
objections  to  the  plain  slide  valve  are  remedied  by  the  use  of 
balanced  valves. 

Balanced  Valves. — The  piston  valve,  illustrated  in  Fig.  65, 
is  one  form  of  balanced  valve.  The  pressures  upon  all  sides  that 
would  force  the  valve  against  its  seat  are  balanced  by  equal 
and  opposite  forces.  When  well  made,  and  properly  fitted  with 
packing  rings,  little  leakage  occurs,  but  small  piston  valves  are 
often  made  without  packing  rings  and  in  such  a  case  leakage  is 
very  likely  to  occur. 


>  STEAM  ENGINES  99 

The  balancing  of  the  flat  slide  valve  is  accomplished  by  the  addi- 
tion of  balancing  plates.  Such  a  device  is  shown  in  Fig.  74.  It 
consists  of  a  machined  plate,  arranged  so  that  it  excludes  the  high 
pressure  steam  from  the  top  of  the  valve.  This  eliminates  the 
pressure  that  would  force  the  valve  upon  its  seat,  and  the  only 
friction  theoretically  present  is  that  due  to  the  weight  of  the 
valve  itself.  Various  valves  employing  this  principle  have  been 
devised.     Some  are  only  partially  balanced.     Others  differ  in  the 


,Balance  Plate 

Steam.  .Chest  ©over 


Piston' 
Fig.  74. — Balanced  valve. 


method  of  maintaining  a  steam  tight  joint  between  the  valve  and 
the  balancing  plate.  The  principle  involved  in  all  balanced 
valves  is  the  same. 

The  Double  Ported  Valve. — One  difficulty  in  the  use  of  the 
plain  slide  valve  is  that  a  large  movement  or  travel  of  the  valve 
is  necessary  in  order  to  fully  open  the  port.  This  makes  it 
difficult  to  use  the  plain  slide  valve  in  engines  having  a  large 
diameter  and  short  stroke.  The  double  ported  valve,  Fig.  75, 
overcomes  this  difficulty.     Instead  of  using  one  large  port  for  the 


100       STEAM  AND  GAS  POWER  ENGINEERING 

passage  of  the  steam,  two  ports,  whose  combined  areas  would 
equal  that  of  a  single  port,  are  used. 


Fig.  75. — Double  ported  valve. 

The  Corliss  Engine. — The  slide  valve  engine  requires  long 
ports  or  passages  for  the  steam.  This  increases  the  amount  of 
surface  to  which  the  steam  is  exposed.  Another  fault  of  the 
slide  valve  is  that  the  same  port  is  used  for  the  live  steam  enter- 


Fig.  76. — Corliss  engine  cylinder  and  valve  gear. 

ing  the  cylinder,  after  it  has  been  cooled  by  the  exhaust  steam. 
To  overcome  these  objections  four-valve  engines  have  been  in- 
troduced. One  of  the  earliest  and  best  of  these  types  is  the  Corliss 
engine. 


STEAM  ENGINES  101 

The  cylinder  of  a  Corliss  engine  is  illustrated  in  Fig.  76.  It 
includes  four  valves,  two  for  the  control  of  the  entering  steam  and 
two  for  the  exhaust.  The  valves  are  cylindrical  in  shape  and  are 
located  at  the  top  and  bottom  of  the  cylinder  at  the  extreme  ends 
of  the  stroke  of  the  engine.  The  steam  and  exhaust  valves  oper- 
ate respectively  in  the  chambers  S  and  E.  The  bell  crank  levers 
D  work  loosely  on  the  valve  stems;  they  are  connected  to  the  wrist 
plate  B  by  the  rods  K.  The  steam  valve  levers  M  are  keyed  to 
the  valve  stem  J,  and  are  also  connected  by  the  rods  0  to  the 
dash  pots  P.  The  bell  crank  levers  D  carry  at  their  outer  ends 
V-shaped  steam  hooks  F}  which  are  provided  with  steel  catch 
plates  that  engage  with  the  arms  M .  The  levers  G  are  connected 
by  the  rods  H  to  the  governor,  and  carry  upon  their  outer  facas 
small  cams  which  release  the  steam  hooks.  The  exhaust  valve 
levers  N  are  connected  directly  through  the  rods  L  to  the  wrist 
plate;  their  motion  being  identical  with  that  of  a  plain  slide 
valve. 

In  the  operation  of  the  engine,  the  wrist  plate  is  given  an  oscil- 
lating motion  by  the  eccentric  to  which  it  is  connected  through  the 
rod  A.  This  causes  the  bell  crank  lever  D  to  oscillate  upward 
and  downward  about  the  spindle  J  as  an  axis.  Upon  the  ex- 
treme downward  movement,  the  steam  hook  engages  the  main 
valve  lever  M,  and  the  upward  movement  of  the  hook  lifts  the 
lever  M  and  opens  the  valve.  The  opening  of  the  valve  continues 
until  the  hook  is  disengaged  by  coming  in  contact  with  the  knock- 
off  cam  on  lever  D.  The  instant  the  valve  is  released,  the  vacuum 
created  in  the  dash  pot  P  causes  the  quick  return  of  the  valve  to 
its  normal  position.  The  governor  controls  the  position  of  the 
knock-off  cam,  thus  regulating,  the  cut-off  by  varying  the  point 
at  which  the  valve  is  released. 

The  trip  gear  described  becomes  impractical  when  the  speed  of 
the  engine  is  high.  Consequently  most  Corliss  engines,  with  the 
trip  or  releasing  valve  gears  operate  at  low  speeds,  usually  about 
85  to  100  revolutions  per  minute. 

Poppet  Valves. — Superheated  steam  decreases  cylinder  con- 
densation and  increases  the  economy  of  the  steam  engine,  but 
highly  superheated  steam  causes  slide  valves  and  those  of  the 
Corliss  type  to  warp.  To  overcome  this  objectionable  feature, 
and  at  the  same  time  to  take  advantage  of  the  gain  that  may  be 


102       STEAM  AND  GAS  POWER  ENGINEERING 

derived  from  superheated  steam,  the  poppet  valve  engine  was 
designed. 

Details  of  one  type  of  poppet  valve  engine  are  shown  in  Fig. 
77.  The  cylinder  has  four  double-seat  poppet  valves,  two  are 
used  for  regulating  the  inlet  steam  and  two  for  regulating  the 
exhaust.  The  operation  of  the  valves  is  accomplished  by  the 
movement  of  an  eccentric  acting  through  a  series  of  levers.  The 
eccentric  is  attached  to  a  lay  shaft,  which  runs  longitudinally 
along  the  outside  of  the  cylinder  and  is  finally  geared  to  the  main 
shaft. 

The  Uniflow  Steam  Engine. — The  reciprocating  steam  engines 
previously  described  are  of  the  counter-flow  or  double-flow 
type.  The  steam,  after  its  expansion  in  this  type  of  engine,  is 
reversed  in  its.  course,  the  cylinder  walls  are  subjected  to  the 
cooling  action  of  the  exhaust  steam  during  the  entire  exhaust 
stroke,  and  the  economy  of  the  engine  is  greatly  decreased  by  the 
losses  due  to  the  condensation  and  re-evaporation  of  the  steam. 
The  uniflow  engine,  Fig.  78,  has  been  designed  to  decrease  the 
above  mentioned  losses.  In  the  uniflow  engine  the  steam  enters 
at  the  ends  of  the  cylinder  as  in  the  counter-flow  engine,  but  is 
exhausted  through  special  ports  arranged  around  the  center  of 
the  cylinder  at  the  farthest  point  from  the  heads.  The  piston 
acts  as  an  exhaust  valve  uncovering  and  covering  the  exhaust 
ports.  The  cylinder  heads  are  exposed  to  the  temperature  of 
the  exhaust  steam  for  a  very  short  time.  The  steam  caught  in 
the  clearance  space  is  compressed  against  the  cylinder  heads, 
which  are  jacketed  with  live  steam.  The  incoming  steam  is  not 
chilled  by  coming  in  contact  with  cool  surfaces,  and  the  losses 
due  to  cylinder  condensation  are  greatly  decreased. 

The  single  cylinder  uniflow  engine  running  condensing  is 
nearly  as  economical  as  a  compound  engine  of  the  counter-flow 
type.  The  uniflow  engine  has  also  shown  remarkable  economy 
at  light  loads. 

Reversing  Engines. — Locomotives,  marine  engines,  hoisting, 
and  other  reversing  engines  must  be  provided  with  a  valve  gear 
by  which  the  direction  of  rotation  may  be  reversed.  The 
Stephenson  link  motion  and  the  Walschaert  radial  valve  gear 
are  the  two  types  most  commonly  used. 

The  Stephenson  link  motion  is  illustrated  in  Fig.  79.     This 


STEAM  ENGINES 


103 


104       STEAM  AND  GAS  POWER  ENGINEERING 


STEAM  ENGINES  105 

motion  makes  use  of  two  eccentrics  A  and  B.  Eccentric  A 
produces  rotation  of  the  engine  in  one  direction  and  is  called  the 
forward  eccentric;  eccentric  B  causes  rotation  in  the  opposite 
direction.  Attached  to  each  eccentric  is  an  eccentric  rod  R, 
which  connects  to  one  end  of  the  slotted  link  L.  The  link  L  is 
connected  to  the  reversing  lever  so  that  its  position  may  be 
varied  at  will.  The  valve  stem  is  attached  to  the  link  block  in 
such  a  manner  that  the  link  is  free  to  move.     Raising  or  lower- 


>£  Lever 


Fig.  79. — Stephenson  link  motion. 

ing  the  link  by  the  reversing  lever  simply  changes  the  position  of 
the  link  with  reference  to  the  link  block  and  the  valve. 

In  the  position  shown,  the  valve  is  controlled  by  the  forward 
eccentric  A.  To  reverse  the  direction  of  rotation,  the  link  L 
must  be  raised  until  the  eccentric  rod  of  the  backing  eccentric 
B  is  directly  in  line  with  the  valve  stem.  The  valve  motion 
would  then  be  controlled  by  the  backing  eccentric,  and 
the  engine  shaft  would  rotate  in  the  opposite  direction. 

If  the  link  is  raised  until  the  valve  stem  is  midway  between  the 


106       STEAM  AND  GAS  POWER  ENGINEERING 


two  ends  of  the  link,  then  the  valve  would  be  affected  equally 
by  both  eccentrics.  When  in  this  position,  very  little  motion  is 
given  to  the  valve. 

The  Walschaeit  valve  gear,  illustrated  in  Fig.  80,  makes  use  of 
a  single  eccentric  placed  at  an  angle  of  90°  with  respect  to  the 
crank.  A  reversing  link  pivoted  at  its  center  is  joined  to  the 
eccentric  by  means  of  the  eccentric  rod  and  to  the  lap  and  lead 
lever  through  the  radius  rod.  The  valve  is  connected  directly 
to  the  lap  and  lead  lever,  which  in  turn  is  connected  to  the  cross- 
head  by  a  small  link. 


Fig.  80. — Walschaert  valve  gear. 

The  motion  derived  from  the  cross-head  moves  the  valve  an 
amount  equal  to  the  lap  plus  the  lead.  The  position  of  the  link 
block  with  respect  to  the  link  is  varied  by  raising  or  lowering 
the  radius  rod.  By  this  means,  the  motion  of  the  engine  can 
be  reversed.  When  the  link  block  is  in  the  mid-position  of  the 
link,  the  motion  derived  from  the  eccentric  is  neutralized  and  the 
valve  is  moved  by  the  cross-head  an  amount  equal  to  the  lap 
plus  the  lead.     A  and  B  show  two  positions  of  valve  gear. 

Condensing  and  Non-condensing  Engines. — Non-condensing 
engines  exhaust  directly  into  the  atmosphere,  into  heating  coils, 
or  into  feed  water  heaters,  where  the  heat  contained  in  the  ex- 


STEAM  ENGINES  107 

haust  steam  is  utilized  in  heating  buildings  or  in  raising  the  tem- 
perature of  the  teed  water,  as  the  case  may  be.  Due  to  the 
frictional  resistance  caused  by  the  steam  flowing  through  the  ex- 
haust ports,  as  well  as  the  resistance  introduced  by  the  piping  and 
other  equipment,  the  pressure  of  the  exhaust  steam  in  non-con- 
densing engines  exceeds  atmospheric  pressure. 

In  the  operation  of  a  condensing  engine,  the  exhaust  steam  from 
the  engine  cylinder  escapes  into  a  condenser,  where  it  is  cooled 
and  condensed  to  water,  thus  producing  a  vacuum  or  a  reduction 
in  the  back  pressure.  The  reduction  in  the  back  pressure  increases 
the  work  done  in  the  cylinder,  if  the  cut-off  remains  constant,  by 
increasing  the  mean  effective  or  unbalanced  pressure.  If  the  cut- 
off is  decreased,  the  same  work  can  be  developed  by  using  a 
smaller  quantity  of  steam. 

Generally  a  condensing  engine  will  use  about  25  per  cent,  less 
steam  than  a  non-condensing  engine  of  the  same  size  on  account 
of  the  lower  back  pressure.  Small  engines  are  very  seldom  oper- 
ated condensing,  as  the  gain  in  economy  is  usually  more  than  bal- 
anced by  the  increased  first  cost  of  the  equipment  and  by  the 
greater  complications  of  the  power  plant.  A  compound  engine 
when  operated  condensing  will  show  a  greater  gain  in  economy,  as 
compared  with  non-condensing  operation,  than  will  a  simple 
engine.  The  uniflow  engine  is  very  economical  when  operated 
condensing.  Where  the  exhaust  steam  can  be  used  for  heat- 
ing or  for  manufacturing  purposes,  the  non-condensing  installa- 
tion is  more  practical. 

Multiple -expansion  Engines. — The  use  of  multiple-expansion 
engines  is  another  method  for  reducing  cylinder  condensation. 
In  the  simple  engine,  in  which  the  total  expansion  of  the  steam 
is  accomplished  in  one  cylinder,  the  cylinder  walls  are  first  ex- 
posed to  the  high  temperature  of  the  inlet  steam  and  then  are 
exposed  to  the  low  temperature  of  the  exhaust  steam.  This 
causes  an  excessive  loss  due  to  the  condensation,  which  can  be 
decreased  by  dividing  the  expansion  into  several  pressure  stages. 

As  there  is  a  direct  relation  between  the  pressure  of  steam  and 
its  temperature,  the  decreasing  of  the  pressure  range  of  steam  in 
a  cylinder  decreases  the  temperature  range  and  hence  decreases 
the  condensation  losses  also.  If  steam,  instead  of  being  expanded 
completely  in  one  cylinder,  is  expanded  down  to  some  inter- 


108       STEAM  AND  GAS  POWER  ENGINEERING 

mediate  pressure  in  one  cylinder  and  then  is  exhausted  into  a 
second  cylinder,  where  its  pressure  is  reduced  to  that  of 
the  exhaust  of  a  simple  engine,  the  temperature  range  and 
condensation  losses  within  each  cylinder  are  decreased.  Such 
an  arrangement  of  cylinders  forms  a  multiple  expansion  engine. 
If  the  pressure  range  takes  place  in  two  stages,  the  engine  is  called 
a  compound;  if  in  three  stages,  triple  expansion;  and  if  in  four 
stages,  quadruple  expansion.  Obviously  the  greater  the  number 
of  pressure  stages,  the  less  will  be  the  temperature  range  and 
hence  the  better  the  economy.  A  triple  expansion  engine  is, 
for  that  reason,  more  economical  than  one  operating  compound, 
but  the  gain  in  economy  when  using  triple  expansion  engines  is 
usually  more  than  offset  by  the  increased  cost  of  the  equipment, 


Fig.  81. — Tandem  compound  engine. 

the  extra  floor  space  required  for  the  additional  cylinder,  and  the 
greater  complications  of  the  power  plant.  Triple  expansion  en- 
gines are  used  in  marine  practice  and  in  pumping  plants,  but 
are  seldom  found  in  steam-electric  power  plants;  ordinarily,  the 
compound  engine  is  preferable  when  conditions  warrant  a  multi- 
ple expansion  engine. 

There  are  two  different  types  of  compound  engines — the  tandem 
and  the  cross  compound.  This  classification  depends  upon  the 
arrangement  of  the  cylinders. 

In  the  tandem  compound  engine,  Fig.  81,  the  axes  of  the  low 
and  high  pressure  cylinders  are  in  one  straight  line.  The  piston 
rod  is  common  to  both  cylinders  and  the  total  force  transmitted 
to  the  single  crank  is  the  sum  of  the  forces  exerted  in  each 
cylinder. 


STEAM  ENGINES 


109 


The  cross  compound  engine,  Fig.  82,  has  its  cylinders  arranged 
side  by  side,  and  the  force  exerted  in  each  cylinder  is  transmitted 
to  the  separate  crank  pins,  usually  set  at  an  angle  of  90°.  By 
this  arrangement,  the  turning  effort  at  the  crank  pin  is  more 
nearly  uniform. 


Fig.  82, — Cross  compound  engine. 


The  Steam  Locomobile. — The  steam  locomobile  is  a  self-con- 
tained power  plant,  which  consists  of  a  compound  steam  engine 
mounted  upon  an  internally  fired '  boiler.  An  insulatep!  sheet- 
metal  smoke  box  incloses  both  engine  cylinders,  a  superheater, 
all  steam  piping  and  valves,  and  a  reheater  which  imparts 
heat  to  the  steam  as  it  passes  from  the  high  pressure  to  the  low 
pressure  cylinder.  This  arrangement  utilizes  the  heat  in  the 
flue  gases  for  superheating  the  steam  before  it  enters  the  engine 
cylinder,  for  reheating  the  steam  between  the  high-  and  the  low- 
pressure  cylinder,  for  reducing  heat  losses  within  the  engine,  and 
for  cutting  down  the  radiation  losses  of  the  entire  power  plant. 

The  steam  from  the  engine  exhausts  through  a  feed-water 
heater  into  a  condenser,  where  it  is  condensed  by  direct  contact 


110       STEAM  AND  GAS  POWER  ENGINEERING 

with  cold  water  or  by  contact  with  tubes  through  which  cole- 
water  circulates. 

Fig.  83  shows  a  longitudinal  section  of  a  steam  locomobile  with 
the  various  parts  named. 


Valve  Setting. — The  object  of  setting  valves  on  an  engine  is 
to  equalize  the  work  done  in  both  ends  of  the  piston.  The 
method  of  procedure  will  vary  with  the  type  of  valve,  but  the 


STEAM  ENGINES 


111 


general  principles  will  be  understood  from  the  following  method 
used  in  setting  the  plain  slide  valve. 

Before  a  valve  can  be  set,  the  dead  centers  for  both  ends  of  the 
engine  must  be  accurately  detei mined. 

The  method  of  setting  an  engine  on  dead  center  can  best  be 
understood  by  referring  to  Fig.  84.  H  represents  the  engine 
crosshead  which  moves  between  the  guides  maiked  G,  N  is  the 
connecting  rod,  R  the  crank,  F  the  engine  flywheel,  and  0  is  a 
stationary  object. 

To  set  the  engine  on  dead  center,  turn  the  engine  in  the  direc- 
tion in  which  it  is  supposed  to  run,  as  shown  by  the  arrow,  until 
the  cross-head  is  near  the  end  of  its  head  end  travel,  and  make 


Fig.  84. — Valve  setting. 


a  small  scratch  mark  on  the  cross-head  and  guide  as  at  A.  At 
the  same  time  mark  the  edge  of  the  flywheel  and  the  stationary 
object  opposite  each  other,  as  at  B.  Turn  the  engine  past  dead 
center,  in  the  same  direction  as  shown  by  the  arrow,  until  the 
mark  on  the  cross-head  and  that  on  the  guide  again  coincide  at 
A,  and  mark  the  flywheel  in  line  with  the  same  point  on  the 
stationary  object,  obtaining  the  mark  C.  The  distance  between 
the  two  marks  on  the  flywheel  is  now  bisected  at  E.  If  the  mark 
E  on  the  flywheel  is  now  placed  in  line  with  the  mark  on  the 
stationary  object,  the  engine  will  be  on  the  head  end  dead  center. 
Similarly,  the  crank  end  dead  center  can  be  found. 

The  stationary  object  may  be  a  wooden  board,  or  a  tram 
may  be  used  with  one  end  resting  on  the  engine  bedplate  and 


112        STEAM  AND  GAS  POWER  ENGINEERING 

with  the  other  end  used  for  locating  the  marks  B,  C,  and  E  on 
the  flywheel. 

One  of  two  methods  may  be  used  in  setting  the  valve.  It  may 
be  set  so  that  both  ends  have  the  same  leads,  or  so  that  the  point 
of  cut-off  is  the  same  at  both  ends. 

If  the  valve  is  to  be  set  for  equal  lead  on  both  ends,  set  the 
engine  on  the  dead  center  by  the  method  given  above,  remove 
the  steam  chest  cover,  and  measure  the  lead  at  that  end.  Move 
the  engine  to  the  other  dead  center  and  measure  the  lead  again. 
If  the  lead  on  the  two  ends  is  not  the  same,  correct  the  difference, 
by  moving  the  valve  on  the  valve  stem. 

To  set  the  engine  for  equal  cut-off,  turn  the  engine  until  the 
valve  cuts-off  at  one  end  and  mark  the  position  of  the  cross-head 
on  the  guides.  Then  turn  the  engine  until  the  cut-off  occurs  on 
the  opposite  end  and  again  mark  this  position  of  the  cross-head 
on  the  guides.  If  the  cut-off  occurs  earlier  at  one  end  than  at  the 
other,  change  the  length  of  the  valve  stem  until  the  cut-off  is 
equalized  at  both  ends. 

Setting  Corliss  Valves. — The  setting  of  Corliss  valves  is  more 
complicated  than  the  setting  of  plain  slide  valves,  but  can  be 
easily  accomplished  if  the  customary  marks  have  been  placed 
upon  the  various  parts  by  the  engine  builder.  The  wrist-plate 
support  (Fig.  856)  is  marked  by  three  lines  a,  c,  and  b,  while  the 
hub  of  the  wrist-plate  itself  is  provided  with  one  line,  d.  These 
three  lines  mark  the  points  of  the  extreme  travel  as  well  as  the 
central  position  of  the  wrist-plate  when  the  mark  d  upon  the 
wrist-plate  hub  coincides  with  its  respective  mark,  a  and  b,  or* 
c  upon  the  support.  When  the  back  bonnets  of  the  valve 
chambers  are  removed,  there  will  be  found  marks,  i  and  j 
(Fig.  85a),  which  coincide  with  the  working  edges  of  each  of  the 
steam  valves.  Similar  marks,  e  and  /,  on  the  face  of  the  steam 
valve  chamber  coincides  with  the  working  edge  of  each  of  the 
steam  ports.  The  exhaust  valves  and  their  chambers  are  marked 
in  a  similar  manner. 

To  set  the  valves,  place  the  wrist-plate  in  its  central  position. 
This  point  is  found  when  the  mark,  d,  upon  the  wrist-plate 
hub  (Fig.  856)  coincides  with  the  central  mark,  c,  upon  the  wrist- 
plate  support.     Fasten  the  wrist-plate  in  this  position  by  placing 


STEAM  ENGINES 


113 


a  piece  of  paper  between  it  and  the  washer  which  holds  the  wrist- 
plate  on  the  stud.  Now  with  the  steam  valves  hooked  up,  adjust 
the  rod  M  (Fig.  85a)  leading  from  the  wrist-plate  to  the  double 
arm  lever  so  that  each  steam  valve  will  have  an  equal  and  slight 
amount  of  lap.  The  amount  of  this  lap  varies  from  34  6"  to 
%",  increasing  with  the  size  of  the  engine.  The  exhaust  valves 
should  be  similarly  adjusted.  After  the  steam  and  exhaust 
valves  have  been  adjusted,  the  paper  between  the  wrist-plate 
and  the  washer  should  be  removed. 


& 


\?- 


t/ 


\  1 
y 

X 

/ 

Wrist 

-Plate 

\ 
\ 
\ 

\ 

1 
1 

1 

\ 

t 

\ 

\ 

V 

/ 

1 
1 

/ 

Engine  Cylinder 


?*'-.. 


Wrist- Plate  Support^  a  f  b 

Wrist-Plate  Hub-> 
Wrbt  Plate* 


& 


e 


( b)  Method  of  Marking  Wrist-Plate  Hub 


(a)  Rear  of  Valves  with  Bonneb  Removed 

Fig.  85. — Diagram  of  Corliss  valve  mechanism. 


The  rocker  arm,  with  the  eccentric  rod  attached,  should  now 
be  placed  in  a  vertical  position  by  means  of  a  plumb  line.  Loosen 
the  eccentric  on  the  shaft  and  adjust  the  eccentric  rod  so  that  the 
extreme  travel  points  of  the  rocker  arm  are  equidistant  from  the 
plumb  line.  Now  connect  the  hook  rod  to  the  wrist-plate  and 
adjust  the  length  of  the  hook  rod  so  that  when  the  eccentric  is 
revolved  on  the  shaft  the  mark  d  (Fig.  856)  upon  the  wrist-plate 
hub  coincides  with  the  extreme  travel  marks  a  and  b  upon  the 
wrist-plate  support. 

To  adjust  the  lead,  place  the  engine  on  one  of  its  dead  centers 
and  turn  the  eccentric  loosely  on  the  shaft  in  the  direction  the 
engine  is  to  rotate  until  the  steam  valve  nearest  the  piston  has 
the  proper  lead.     Now  secure  the  eccentric  to  the  shaft. 

8 


114        STEAM  AND  GAS  POWER  ENGINEERING 

To  adjust  the  cut-off,  secure  the  governor  in  its  highest  posi- 
tion and  disconnect  the  wrist-plate  from  the  eccentric.  Adjust 
the  governor  cam  rods,  so  that,  as  the  wrist-plate  is  oscillated, 
the  releasing  of  the  steam  valves  in  each  end  of  the  cylinder  occurs 
when  the  port  is  open  about  }>i  inch.  With  the  governor  in  its 
lowest  working  position,  the  releasing  gear  should  not  detach 
the  steam  valves. 

Replace  the  valve  bonnets  and  see  that  all  connections  have 
been  properly  made.  It  is  always  best  to  oscillate  the  wrist- 
plate  a  few  times  to  see  that  the  hooks  engage  properly  and  that 
the  dash  pot  rods  are  adjusted  to  a  proper  length. 

Horsepower. — The  measurement  of  the  power  of  an  engine  is 
in  terms  of  horsepower.  If  work  is  done  at  the  rate  of  33,000 
foot-pounds  per  minute,  one  horsepower  is  said  to  be  developed. 

Power  takes  into  consideration  the  time  required  to  do  a 
certain  amount  of  work  and  is  denned  as  the  rate  of  doing  work. 
Work  means  force  times  distance  through  which  it  acts  and  is 
independent  of  time.  Thus  if  steam  at  a  pressure  of  100  pounds 
moves  a  piston  18  in.  in  diameter  through  a  distance  oi  2  ft.,  the 
work  done  is  100  times  508.92  (the  area  of  the  piston  in  inches 
multiplied  by  the  distance  in  feet)  or  50,892  ft.-lb.  The  power 
of  the  engine,  however,  depends  on  the  time  that  the  steam 
requires  to  move  the  piston  through  the  given  distance  and,  if  the 
motion  is  accomplished  in  1  second,  the  power  of  the  engine  is 
five  times  greater  than  if  5  seconds  were  required. 

An  engine  will  have  a  capacity  of  1  hp.  if  it  can  do  550  ft.-lb.  of 
work  in  a  second,  33,000  ft.-lb.  of  work  in  a  minute,  or  1,980,000  ft.- 
lb.  of  work  in  an  hour.  To  determine  the  horsepower  developed 
by  any  motor  or  engine,  it  is  necessary  to  find  the  foot-pounds 
of  work  which  the  motor  or  engine  is  doing  in  a  minute  and  divide 
this  by  33,000.  In  the  example  of  the  previous  paragraph,  if  the 
piston  passes  through  the  distance  of  2  ft.  in  J£o  min.,  the  power 
of  the  engine  in  horsepower  is: 

50,8921        =  n 


33,000  X  Ho 


Indicated  Horsepower. — The  term  "indicated  horsepower'* 
(I.hp.)  is  applied  to  the  rate  of  doing  work  by  steam  or  gas  in 
the  cylinder  of  an  engine,  and  is  obtained  by  means  of  a  special 


STEAM  ENGINES 


115 


instrument,  called  an  indicator.  The  indicator  diagrams  which 
result  from  the  use  of  such  an  instrument  show  graphically  the 
action  of  the  steam  within  the  engine  cylinder,  recording  the 
actual  pressure  at  each  interval  of  the  stroke. 

One  type  of  indicator  is  shown  in  section  in  Fig.  86.  It 
consists  essentially  of  a  cylinder  (4),  which  is  placed  in  direct 
communication  with  the  engine  cylinder.  Within  the  cylinder 
is  the  piston  (8)  to  which  is  attached  a  spring;  as  the  com- 
pression of  the  spring  is  proportional  to  the  pressure  of  the 


Fig.  86. — Steam  engine  indicator. 


steam,  the  movement  of  the  indicator  piston  is  directly  propor- 
tional to  the  pressure  exerted  by  the  steam.  The  piston  is 
attached  to  the  arm  ( 16).  At  the  end  of  the  arm  is  a  small  pencil 
(23)  which  records  the  movement  of  the  piston  and  graphically 
indicates  the  pressure  of  the  steam  within  the  cylinder.  At- 
tached to  the  cylinder  (4)  is  an  arm  which  carries  the  drum  (24). 
A  small  paper  card  to  record  the  motion  of  the  pencil  is  placed 
around  this  drum.  The  drum  is  connected  to  the  cross-head 
of  the  engine,  and  is  provided  with  a  spiral  spring,  which  returns 


116        STEAM  AND  GAS  POWER  ENGINEERING 


it  to  its  original  position  after  being  moved  outward  by  the 
crosshead. 

As  the  diagram  drawn  upon  the  drum  of  the  indicator  re- 
cords the  pressure  at  every  instant  of  the  travel  of  the  piston, 
the  average  unbalanced  pressure,  called  the  mean  effective 
pressure,  may  be  determined  and  the  horsepower  calculated. 

As  an  illustration:  A  steam  pump  in  which  a  valve  without 
laps  is  used  has  the  theoretical  indicator  card  illustrated  in  Fig. 
87.  The  effective  pressure  is  constant  throughout  the  stroke 
and  equals  100  lb.  per  sq.  in.  This  pressure  acts  upon  a  12-in. 
(113.1  sq.  in.  area)  piston.  Then  the  total  pressure  exerted 
by  the  steam  is : 


k 

<5> 


*5 


5f-ectm  Pressure  Line 


■Back  Pressure  Line 


<•-  Atmospheric  Line 
Fig.  87. —  Theoretical  indicator  card  from  direct-acting  steam  pump. 

Total  pressure  =  100  X  113.1  =  11,310  pounds. 
If  the  stroke  of  the  piston  is  12  inches,  the  work  done  in 
foot-pounds  per  stroke  is: 

11,310  X  j| •-  11,310. 

If  this  work  is  exerted  upon  the  piston  50  times  per  minute,  the 
work  the  engine  will  do  per  minute,  if  it  is  single  acting,  will  be : 

11,310  X  50  =  565,500  ft.-lb. 
Since  33,000  ft.-lb.  per  minute  is  1  hp.,  the  power  of  the  engine 
when  single-acting  is: 

565,500 


33,000 


=  17.1 1.hp. 


As  steam  engines  are  usually  double-acting,  an  indicator  card 
would  have  to  be  taken  of  the  crank  end,  as  well  as  of  the  head 
end,  the  unbalanced  or  the  mean  effective  pressure  determined 
for  that  end,  and  the  indicated  horsepower  calculated  by  the 
above  method,   taking  into  consideration  the  size  of  the  piston 


STEAM  ENGINES 


117 


rod.     The  total  indicated  horsepower  of  the  engine  is  the  sum  of 
that  calculated  for  the  two  ends. 

Indicator  Reducing  Motions. — The  diameter  of  the  indicator 
drum  is  such  that  the  motion  of  the  drum  can  only  be  about 
four  inches.  In  driving  the  drum  from  a  cross-head,  whose 
motion  is  in  excess  of  this  amount,  it  is  necessary  to  insert  some 
form  of  reducing  motion.  In  other  words,  some  arrangement  is 
necessary  that  will  reduce  the  motion  of  the  cross-head  so  that  it 
may  be  reproduced  to  a  smaller  scale  on  the  indicator  diagram. 


♦Cord  to  Indicator 


Fig.  88. — Pendulum  reducing  motion. 

Many  indicator  reducing  motions  have  been  devised,  but  many  of 
these  do  not  produce  a  true  reduction.  The  test  of  a  true  reduc- 
tion is  that,  when  the  cross-head  has  moved  any  fraction  of  its 
stroke,  the  indicator  drum  has  been  moved  the  same  fraction  of 
its  total  distance,  as  measured  from  one  of  its  extreme  positions. 
One  type  of  reducing  motion  is  illustrated  in  Fig.  88,  and 
is  often  referred  to  as  the  pendulum  reducing  motion.  The 
pendulum  arm  A B  is  attached  to  the  frame  of  the  engine  at  A. 
Its  lower  end  is  attached  to  the  cross-head  at  H,  through  the 
short  link.  The  string  to  the  indicator  drum  is  attached  to  the 
arm  A  B  at  such  a  point  that  the  proper  reduction  in  the  motion  of 
the  cross-head  is  produced.  This  form  of  motion  is  slightly  in 
error,  due  to  the  vertical  movement  of  the  point  to  which  the 
string  is  attached. 


118       STEAM  AND  GAS  POWER  ENGINEERING 

A  type  of  reducing  motion,  called  a  reducing  wheel,  is  illustrated 
in  Fig.  89.  This  type  of  reducing  motion  is  attached  directly  to 
the  base  of  the  indicator  and  thus  eliminates  any  complicated 
connections  to  the  cross-head  that  are  necessary  with  other  types. 
The  reducing  motion  consists  of  two  wheels  whose  diameters  may 
be  proportioned  to  the  stroke  of  the  engine  and  are  connected 
to  each  other  through  gears.     The  cord  from  the  indicator  drum 


Fig 


Reducing  wheel  attached  to  indicator. 


is  attached  to  the  smaller  wheel,  while  the  larger  wheel  is  con- 
nected to  the  cross-head.  Changing  the  diameters  of  the  two 
wheels  permits  of  indicating  engines  having  strokes  between 
wide  limits. 

The  Indicator  Card. — A  card  taken  from  a  steam  engine  by 
means  ot  an  indicator  is  shown  in  Fig.  90.  The  total  length  of 
the  card  is  proportional  to  the  stroke  of  the  engine,  and  the 
height  at  any  point  is  proportional  to  the  pressure  of  the  steam 


STEAM  ENGINES  119 

in  the  cylinder.  The  events  of  the  stroke  in  the  card  are  marked : 
admission  A,  cut-off  C,  release  R,  compression  K.  The  pressure 
may  be  measured  at  any  point  on  this  card  if  the  scale  of  the 
spring  is  known.  Springs  are  provided  so  that  various  pres- 
sures are  required  to  compress  the  spring  sufficiently  to  cause 
the  pencil  to  be  moved  1  inch.  A  60-pound  spring,  for  in- 
stance, will  require  a  pressure  of  60  pounds  per  sq.  in.  to  cause 
the  pencil  point  to  move  1  inch.  Or  conversely,  if  the  height 
of  an  indicator  card  is  1J^  inches  at  some  point  in  the  diagram 
and  a  60-pound  spring  is  used  in  making  the  card,  the  pressure 
exerted  by  the  steam  in  the  cylinder  is: 

60  X  1M  =  90  pounds  per  sq.  in. 


Fig.  90. — Steam  engine  indicator  card. 

The  Measurement  of  Power  from  Indicator  Cards. — A  close 
analysis  of  an  indicator  card  will  show  that  certain  pressures 
are  exerted  in  the  cylinder  during  the  forward  stroke  and  that 
lesser  pressures  exist  in  the  cylinder  during  the  return  stroke. 
The  two  series  of  pressures  differ  in  that  those  exerted  during 
the  forward  stroke  act  upon  the  piston  of  the  engine  and  are 
transmitted  to  the  main  shaft  or  flywheel,  while  on  the  return 
stroke  the  engine  itself,  due  to  the  momentum  which  has  been 
stored  in  the  various  parts  during  the  forward  stroke,  must  force 
the  steam  out  of  the  cylinder  and  compress  it.  Thus  the  total 
forward  pressure  exerted  in  the  cylinder  is  not  effective  in 
producing  power,  but  some  must  be  utilized  to  exhaust  the  steam 
and  to  produce  the  compression.  The  effective  pressure  is  the 
difference  between  the  total  pressure  and  the  back  pressure.  This 
difference  is  graphically  represented  by  the  pressure  within 
the  indicator  diagram.     To  use  this  value  in  determining   the 


120        STEAM  AND  GAS  POWER  ENGINEERING 

foot-pounds  of  work,  it  must  be  reduced  to  the  mean  effective 
pressure  exerted  throughout  the  stroke.  The  mean  effective  pres- 
sure (M.E.P.)  can  best  be  found  by  the  use  of  a  planimeter,  Fig. 
91,  which  is  an  instrument  for  measuring  areas.     Thus 

M.E.P.  =  i       rr    f -j  X  scale  of  spring. 

length  of  card 


Fig.  91. — Polar  planimeter. 

Another  means  often  employed  in  the  absence  of  a  planimeter  is 
to  divide  the  length  of  the  card  into  10  equal  parts,  as  shown  in 
Fig.  92,  and  obtain  the  average  of  the  heights  in  inches  of  the  10 
trapezoids  formed.     Thus  from  Fig.  92 

a+b+a+d+e+f+g+h+i+j 
10 


M.E.P. 


X  scale  of  spring. 


Fig.  92. — Ordinate  method  of  measuring  mean  effective  pressure. 
The  indicated  horsepower  developed  by  one  end  of  the  cylinder 


is: 


plan 
33,000 

Where  p  =  mean  effective  pressure  in  pounds  per  sq.  in. 
I  =  length  of  stroke  in  feet 
a  =  area  of  piston  in  square  inches 
n  =  number  of  revolutions  per  minute 


STEAM  ENGINES 


121 


In  the  crank  end  of  the  cylinder  this  same  formula  will  apply 
with  the  exception  that  the  effective  area  of  the  piston  is  reduced 
by  the  area  of  the  piston  rod. 

As  an  illustration,  the  following  data  was  obtained  from  the 
test  of  a  steam  engine: 

Diameter  of  engine  cylinder  10  inches  (area  78.54  sq.  in.). 

Diameter    of    piston    rod    1%   inches    (area   2.405   sq.    in.) 

Stroke  of  engine  12  inches 

Speed  of  engine  280  r.p.m. 

If  the  mean  effective  pressure  in  the  head  end  side  of  the  cylin- 
der is  found  to  be  41.64. 

The  I.hp.  in  the  head  end  side  is  then: 

41.64  X  ~  X  78.54  X  280 

33,000  =  27.73  hp. 

The  indicated  horsepower  in  the  crank  end  side  of  the  cylinder 
is  obtained  in  the  same  manner,  but  the  effective  area  in  this 
side  of  the  cylinder,  which  is  found  by  deducting  the  area  of  the 
piston  rod,  must  be  used. 

If   the   mean   effective   pressure   in  the  crank  end  is  35.76, 
the  I.hp.  in  the  crank  end  is  then: 
12 


35.76  X  j=  X  (78.54  -  2.405)  X  280 


=  23.10  hp. 


33,000 
The  total  indicated  horsepower  developed  by  the  engine  is: 

27.73  +  23.10  =  50.83  hp. 
Valve  Setting  by  Indicator  Cards. — In  general,  one  of  the  best 
methods  of  setting  the  valve  of  a  steam  engine  is  by  means  of  the 


Fig.  93.  — Indicator   cards, 
valves  properly  set. 


Fig.  94.  —  Indicator   cards, 
valves  improperly  set. 


steam  engine  indicator.  Any  distortion  in  the  events  of  the 
stroke  is  easily  detected,  and  a  little  study  of  such  diagrams 
suggests  the  proper  steps  to  correct  the  difficulty. 


122        STEAM  AND  GAS  POWER  ENGINEERING 


Fig.  93  shows  indicator  cards  taken  from  the  two  ends  of  a 
cylinder  when  the  valve  is  properly  set.     The  four  events  in 

each  cylinder  occur  at  very 
nearly  the  same  point  in  each 
stroke,  and  the  cards  compare 
favorably  with  that  of  an  ideal 
diagram. 

Fig.  94  shows  indicator  cards 
taken  from  two  ends  of  a  cyl- 
inder when  the  valve  is  poorly 
set.  Comparing  the  cards  from 
the  two  ends  of  the  cylinder, 
the  same  events  in  the  two  ends 
occur  at  different  points  in  the 
stroke;  this  indicates  that  an 
adjustment  of  the  valve  is 
necessary. 

Fig.  95  shows  samples  of 
good  and  imperfect  indicator 
diagrams.  The  cause  of  each 
defect  is  explained. 

Brake  Horsepower. — Brake 
horsepower  represents  the 
actual  effective  power  which  a 
motor  or  engine  can  deliver  for 
the  purpose  of  work  at  a  shaft 
or  a  brake.  An  instrument  for 
the  measurement  of  the  brake 
horsepower  of  motors,  called  a 
Prony  brake,  is  shown  in  Fig. 
96.  This  brake  consists  of  two 
wooden  blocks  BB  which  fit 
around  the  pulley  P,  and  are 
tightened  by  means  of  the 
thumb  nuts  NN.  A  projec- 
tion of  one  of  the  blocks,  the 
lever  L,  rests  on  the  platform 
scale  S.  When  the  brake  is  balanced,  the  power  absorbed  is 
measured  by  the  weight,  as  registered  on  the  scales,  multiplied 


STEAM  ENGINES 


123 


by  the  distance  through  which  it  would  pass  in  a  given  time 
if  free  to  move.  If  I  is  the  length  of  the  brake  arm  in  feet, 
measured  from  the  center  of  the  shaft  to  the  point  of  support  on 
the  scales,  w  the  net  weight  as  registered  on  the  scales  in  pounds, 
and  n  the  revolutions  per  minute  of  the  motor,  the  horsepower 
absorbed  can  be  calculated  by  the  formula: 

Brake  horsepower  = 

As  an  illustration,  the  net  scale  reading  of  an  engine  running  at  250 
r.p.m.  is  80  lb.  If  the  length  of  the  brake  arm  is  5J4  feet,  cal- 
culate the  brake  horsepower  developed. 

2  X  3.1416  X  5.25  X  80  X  250 


Brake  horsepower  = 


33,000 


20.00 


Fig.  96. — Prony  brake. 

Friction  Horsepower. — The  indicated  horsepower  of  an  engine 
would  be  equal  to  that  of  the  brake  horsepower  if  no  losses  oc- 
curred in  the  machine.  The  indicated  horsepower  is,  however, 
always  in  excess  of  the  brake  horsepower  by  an  amount  equiva- 
lent to  the  power  consumed  in  friction.  The  difference  between 
the  indicated  horsepower  and  the  brake  horsepower  is  conse- 
quently the  friction  horsepower. 

F.hp.  =  I.hp.  -  B.hp. 

Mechanical  Efficiency. — The  mechanical  efficiency  of  an  engine 
is  the  ratio  of  the  brake  horsepower  (B.hp.)  to  the  indicated 
horsepower  (I.hp.). 

B.hp. 


Mech.  efficiency  = 


I.hp. 


124        STEAM  AND  GAS  POWER  ENGINEERING 

The  mechanical  efficiency  is  the  percentage  of  the  indicated  horse- 
power that  is  delivered  to  the  shaft  as  effective  work.  One 
hundred  minus  the  per  cent,  mechanical  efficiency  gives  the  per- 
centage of  the  indicated  horsepower  that  is  lost  in  friction. 

Steam-engine  Governors. — The  function  of  a  governor  is  to 
control  the  speed  of  rotation  of  a  motor  irrespective  of  the  power 
which  it  develops.  In  the  steam  engine  the  governor  maintains 
a  uniform  speed  of  rotation  either  by  varying  the  initial  pressure 


Fig.  97. — Steam  engine  governor. 


of  the  steam  supplied,  or  by  changing  the  point  of  cut-off  and 
hence  the  portion  of  the  stroke  during  which  steam  is  admitted. 
Governors  which  regulate  the  speed  of  an  engine  by  varying 
the  initial  pressure  of  the  steam  supplied  to  the  engine  are  called 
throttling  governors.  The  throttling  governor  is  the  simplest 
form  of  governor,  and  is  used  mainly  on  engines  of  the  plain 
slide-valve  type.  In  Fig.  97  is  given  a  section  of  a  throttling 
governor,  showing  details.  This  form  of  governor  is  attached  to 
the  steam  pipe  at  A,  and  is  connected  to  the  engine  cylinder  at 
B,  so  that  the  steam  must  pass  the  valve  V  before  entering  the 


STEAM  ENGINES 


125 


engine.  The  valve  V  is  a  balanced  valve  and  is  attached  to  a 
valve  stem  S,  at  the  upper  end  of  which  are  two  balls  CC.  The 
valve  stem  and  balls  are  driven  from  the  engine  shaft  by  a  belt, 
which  is  connected  to  the  pulley  P,  and  which  in  turn  runs  the 
bevel  gears  D  and  E.  As  the  speed  of  the  engine  is  increased 
the  centrifugal  force  makes  the  balls  fly  out,  and  in  doing  so 
they  force  down  the  valve  stem  S,  thus  reducing  the  area  of  the 
opening  through  the  valve,  and  the  steam  to  the  engine  is 
throttled.  As  soon  as  the  engine  begins  to  slow  down,  the  balls 
drop,  increasing  the  steam  opening  through  the  valve  V.     The 


A* 

**. 

y'   1 

A 

D   ^ 

spr 

Fk 


-Shaft  governor. 


speed  at  which  the  steam  is  throttled  can  be  changed  within 
certain  limits  by  regulating  the  position  of  the  balls  by  means 
of  the  nut  N. 

Most  of  the  better  engines  are  governed  by  varying  the  point 
of  cut-oft  and  hence  the  total  volume  of  steam  supplied  to  the 
cylinder.  In  high-speed  automatic  engines  this  is  accomplished 
by  some  form  of  flywheel  or  shaft  governor,  which  controls  the 
point  of  cut-off  by  changing  the  position  of  the  eccentric. 

One  form  of  flywheel  governor  is  shown  in  Fig.  98.  The  sheave 
of  the  eccentric  is  mounted  upon  an  arm  which  is  pivoted  to  the 
flywheel.  The  eccentric  sheave  contains  a  slot  which  passes 
over  the  shaft,  and  the  outer  end  of  the  arm  is  attached  to  the 
weight  as  shown.     In  the  operation  of  the  governor,  centrifugal 


126        STEAM  AND  GAS  POWER  ENGINEERING 

force  causes  a  movement  of  the  governor  weight,  and  in  so  doing 
the  position  of  the  eccentric  and  hence  the  cut-off  is  changed. 
As  the  speed  of  the  engine  increases,  the  cut-off  is  reduced;  and 
when  the  speed  slows  down  the  cut-off  is  increased. 

Engine  Details. — The  general  construction  of  steam-engine 
cylinders  can  be  seen  from  the  previous  illustrations.     Steam- 


Fig.  99. — Steam  engine  piston. 

engine  cylinders  are  made  of  cast  iron.  As  the  cylinder  wears, 
it  has  to  be  rebored  so  as  to  maintain  true  inside  surfaces.  The 
thickness  of  the  cylinder  walls  should  be  not  only  sufficient  to 
withstand  safely  the  maximum  steam  pressure,  but  should  allow 
for  reboring.  All  steam-engine  cylinders  should  be  provided  with 
drip  cocks  at  each  end  in  order  to  drain  the  cylinder  and  steam 
chest  when  starting. 


Fig.  100. — Steam  engine  cross-b 

A  good  piston  should  be  steam  tight  and  at  the  same  time 
should  not  produce  too  much  friction  when  sliding  inside  the 
engine  cylinder.  The  piston  is  usually  constructed  somewhat 
smaller  than  the  inside  diameter  of  the  engine  cylinder,  and  is 
made  tight  by  the  use  of  split  cast-iron  packing  rings.  In  Fig. 
99  is  illustrated  a  piston  with  its  packing  rings. 


STEAM  ENGINES 


127 


The  general  construction  of  steam-engine  cross-heads  is  illus- 
trated in  Fig.  100.  All  cross-heads  should  be  provided  with 
shoes  which  can  be  adjusted  for  wear. 


Fig.   101. — Steam  engine  connecting  rod. 

Fig.  101  shows  a  connecting  rod.  A  connecting  rod  should 
be  so  constructed  that  the  wear  on  its  bearings  can  be  taken 
up.  This  is  usually  accomplished  by  wedges  and  set-screws  as 
illustrated. 


@» 


Fig.  102  — Eccentric  rod  and  strap. 

Some  engines  have  their  cranks  located  between  the  two  bear- 
ings of  an  engine,  and  are  called  center-crank  engines.  Engines 
which  have  their  cranks  located  at  the  end  of  the  shaft  and  on 
one  side  of  the  two  bearings  are  called  side-crank  engines. 


Fig.  103. — Main  bearings. 

The  eccentric  is  a  special  form  of  crank.     It  is  usually  set 
somewhat  more  than  90°  ahead  of  the  crank  and  gives  motion  to 


128        STEAM  AND  GAS  POWER  ENGINEERING 


the  valve  or  valves  in  the  steam  chest  of  the  engine.     Fig.  102 
shows  an  eccentric  rod  and  strap. 

The  main  bearings  of  steam  engines  are  illustrated  in  Fig.  103. 
These  bearings  are  usually  made  in  three  or  four  parts  and  can 
be  adjusted  for  wear  by  means  of  wedges  and  setscrews  fastened 
with  locknuts. 

Lubricators. — The  function  of  lubrication  is  to  decrease  the 
frictional  losses  which  occur  in  steam  engine  operation.  All 
rubbing  surfaces  at  which  friction  is  produced  must  be  lubricated. 

Bearings  maybe  lubricated  by 
grease  cups  as  illustrated  in  Figs. 
104  and  105.  The  first  type  is 
used  on  stationary  bearings,  the 
grease  being  forced  out  by  screw- 


Fig.  104.—  Grease  cups. 


Fig.  105. — Automatic  grease  cup. 


ing  the  cap  down  by  hand.  The  type  illustrated  in  Fig.  105  is 
automatically  operated,  and  is  used  for  the  lubrication  of 
crankpins. 

If  oil  is  used,  a  sight-feed  lubricator  is  employed,  as  shown  in 
Fig.  106.  By  means  of  the  sight-feed  types  the  flow  of  oil  can 
be  regulated  and  the  drops  of  oil  issuing  from  the  lubricator  can 
be  seen. 

For  the  lubrication  of  steam-engine  cylinders  some  form  of 
sight-feed  automatic  steam  lubricator,  as  illustrated  in  Fig.  107, 
should  be  employed.  This  form  of  lubricator  is  used  to  introduce 
a  heavy  oil  into  the  steam  entering  the  cylinder.  This  oil  is  a 
specially  refined  heavy  petroleum  oil  which  will  neither  decom- 
pose, vaporize,  nor  burn  when  exposed  to  the  high  temperature  of 
steam.  Steam  from  the  pipe  B  leading  to  the  engine  cylinder 
is  admitted  through  the  pipe  F  to  the  condensing  chamber  L, 


STEAM  ENGINES 


129 


where  it  is  condensed  and  flows  through  the  pipe  P  to  the  bottom 
of  the  chamber  A.  The  oil  which  is  contained  in  chamber  A  rises 
to  the  top,  is  forced  through  the  tube  S,  ascends  in  drops  through 
the  water  in  the  gage  glass  H,  and  into  the  steam  pipe  K  leading 
to  the  steam  chest.  The  amount  of  oil  fed  is  regulated  by  the 
needle  valve  E.  The  gage  glass  J  shows  the  amount  of  oil  in 
the  chamber  A.  In  order  to  fill  the  chamber  A,  the  valves  on 
the  pipes  F  and  II  are  closed,  the  water  is  drained  out  through 
G,  and  the  cap  D  is  removed  for  receiving  the  oil. 


Fig.  106. — Sight-feed  lubricator.    Fig.  107. — Sight-feed  automatic  lubricator. 

Steam  Engine  Economy. — The  economy  of  steam  engines  is 
usually  expressed  in  pounds  of  steam  consumed  per  horsepower 
per  hour.  In  the  case  of  steam-electric  power  plants  the  economy 
is  expressed  in  pounds  of  steam  consumed  per  kilowatt-hour. 
The  steam  consumption  of  simple,  non-condensing  engines  will 
vary,  under  good  operating  conditions  and  at  full  load,  from  20 
to  35  pounds  per  horsepower  per  hour,  depending  upon  the  type 
of  valve  gear  used.  Compound  condensing  engines  consume 
12  to  20  pounds  of  steam  per  horsepower  per  hour. 

Reciprocating  steam  engines  are  usually  operated  at  steam 
pressures  varying  from  75  to  200  pounds  per  square  inch.  The 
gain  produced  in  economy  by  increasing  the  steam  pressure  from 
80  to  100  pounds  per  square  inch  is  about  twice  as  great  as  that 
resulting  from  increasing  the  steam  pressure  from  180  to  200 
pounds  per  square  inch.  In  general,  the  practical  limit  for  steam 
9 


130        STEAM  AND  GAS  POWER  ENGINEERING 

pressure  is  mainly  one  of  expense.  The  first  cost  and  the  cost 
of  upkeep  of  steam  power  plant  equipment  increases  with  the 
steam  pressure. 

The  exhaust  pressure  at  which  an  engine  is  operated  depends 
upon  the  use  to  which  the  exhaust  steam  can  be  put.  If  the 
exhaust  steam  can  be  used  for  heating  or  for  manufacturing 
purposes  engines  are  operated  non-condensing.  With  large  com- 
pound engines  the  gain  due  to  condensing  is  considerable.  Con- 
densing reciprocating  engines  give  best  economy  with  back 
pressures  of  about  two  pounds  absolute  (26  inches  vacuum). 

The  quality  of  the  steam  influences  the  losses  due  to  conden- 
sation and  re-evaporation.  The  use  of  superheated  steam,  con- 
sidering the  cost  of  producing  the  superheat,  will  increase  the  net 
economy  of  steam  engines  by  about  5  per  cent,  for  every  100 
degrees  superheat. 

Installation  and  Care  of  Steam  Engines. — Foundations  for 
stationary  steam  engines  are  usually  put  in  by  the  purchaser, 
the  manufacturer  furnishing  complete  drawings  for  that  purpose. 
Drawings  of  a  board  template  are  also  included.  A  template 
is  a  wooden  frame  which  is  used  in  locating  the  foundation  bolts 
and  for  holding  them  in  position  while  building  the  foundation. 

Before  starting  on  the  foundation  a  bed  should  be  prepared  for 
receiving  it.  The  depth  of  bed  depends  on  the  soil.  If  the  soil 
is  rocky  and  firm,  the  foundation  can  be  built  without  much  diffi- 
culty.    When  the  soil  is  very  soft,  piles  may  have  to  be  driven. 

The  wooden  template  is  then  constructed  from  the  drawings, 
holes  being  bored  for  the  insertion  of  foundation  bolts. 

Foundations  are  usually  built  of  concrete.  The  concrete 
mixture  should  consist  of  1  part  of  cement,  2  parts  of  sharp 
sand,  and  4  parts  of  crushed  stone.  The  stone  should 
be  of  a  size  as  will  pass  through  a  2-inch  ring.  In  starting  on  a 
concrete  foundation,  a  wooden  frame  of  the  exact  shape  of  the 
foundation  is  built.  The  template  is  then  placed  in  position  in 
the  manner  shown  by  Fig.  108,  and  the  bolts  are  put  in,  the  heads 
of  the  bolts  being  at  the  bottom  in  recesses  of  cast  iron  anchor 
plates  marked  P.  Often  the  foundation  bolts  are  threaded  at 
both  ends  and  the  anchor  plates  are  held  in  place  by  square  nuts. 
A  piece  of  pipe  should  be  placed  around  each  bolt,  so  as  to  allow 
the  bolts  to  be  moved  slightly  to  pass  through  the  holes  in  the 


STEAM  ENGINES 


131 


engine  bedplate,  in  case  an  error  should  occur  in  the  placing  of 
the  bolts,  or  in  the  location  of  the  bolt  holes  in  the  engine  bed- 
plate. 

With  the  frame,  template,  and  foundation  bolts  in  place,  the 
concrete  can  now  be  poured  and  tamped  down.  After  the  con- 
crete has  set,  the  template  is  removed  and  the  loundation  is  made 
perfectly  level.  It  is  well  to  allow  a  concrete  foundation  to  set 
several  weeks  before  placing  the  full  weight  of  the  engine  on  it. 

When  the  foundation  is  ready,  the  engine  is  placed  in  position 
and  leveled  by  means  of  wedges  The  nuts  on  the  bolts  are 
now  screwed  down  and  the  engine  is  grouted  in  place  by  means  of 
neat  cement,  this  serving  to  fill  any  crevices  and  to  give  the  en- 
gine a  perfect  bearing  on  the  foundation. 


Fig.  108. — Foundation  in  the  process  of  construction. 


After  erecting  the  engine  and  all  its  auxiliaries,  including  pipes, 
valves,  cocks,  and  lubricators,  all  the  parts  should  be  carefully 
examined  and  cleaned,  and  a  coating  of  oil  should  be  applied 
to  all  rubbing  surfaces,  cylinder  oil  being  used  for  the  wearing 
parts  in  the  valve  chest  and  cylinder. 

Before  the  engine  is  operated  for  the  first  time,  it  is  well  to 
adjust  bearings,  and  turn  the  engine  over  slowly  until  an  oppor- 
tunity has  been  given  for  any  inequalities  due  to  tool  and  file 
marks  to  be  partially  eliminated,  and  also  to  prevent  heating 
that  might  occur  if  there  was  an  error  in  adjustment. 

When  the  engine  is  ready  to  start,  the  steam  throttle  valve  should 
be  slowly  opened  to  allow  the  piping  to  warm  up,  but  leaving 
the  drain  cock  in  the  steam  pipe,  above  the  steam  chest,  open  to 


132        STEAM  AND  GAS  POWER  ENGINEERING 

permit  the  escape  of  condensation.  While  the  piping  is  being 
warmed  up  all  the  grease  cups  and  lubricators  are  filled.  Before 
opening  the  throttle  valve,  all  cylinder  and  steam-chest  drain 
cocks  should  be  opened  to  expel  water,  and  the  flow  of  oil  started 
through  the  various  lubricators.  The  throttle  valve  is  then 
opened  gradually,  and  both  ends  of  the  engine  warmed  up.  This 
can  be  accomplished  in  the  case  of  a  single-valve  engine  by  turn- 
ing the  engine  over  slowly  by  hand  to  admit  steam  in  turn  to 
each  end  of  the  cylinder.  In  starting  a  Corliss  engine  the  eccen- 
tric is  disconnected  from  the  wrist-plate  and  the  wrist-plate  is 
rocked  by  hand  sufficiently  to  allow  steam  to  pass  through  each 
set  of  valves.  The  drain  cocks  are  closed  soon  after  the  throttle 
is  wide  open  and  the  engine  is  gradually  brought  up  to  speed. 

When  stopping  an  engine,  close  the  throttle  valve.  As  soon 
as  the  engine  stops,  close  the  lubricators,  wipe  clean  the  various 
parts,  examine  all  bearings,  and  leave  the  engine  in  perfect 
condition  ready  to  start. 

The  above  instructions  apply  to  non-condensing  engines.  If 
the  engine  is  to  be  operated  condensing,  the  circulating  and  air 
pumps  should  be  started  while  the  engine  is  warming  up.  The 
other  directions  apply  with  slight  modifications  to  all  types  of 
steam  engines. 

In  regard  to  daily  operation,  cleanliness  is  of  great  importance. 
No  part  of  the  engine  should  be  allowed  to  become  dirty  and  all 
parts  must  be  kept  free  from  rust.  It  is  well  to  draw  off  all 
the  oil  from  bearings  quite  frequently  and  to  clean  them  with 
kerosene  before  refilling  with  fresh  oil.  In  starting  it  is  well  to 
give  the  various  parts  plenty  of  oil,  but  the  amount  should  be 
decreased  as  the  engine  warms  up.  An  excess  of  oil  should  be 
avoided. 

Competent  engine  operators  usually  make  a  practice  of  going 
over  and  cleaning  every  bearing,  nut,  and  bolt,  immediately 
on  shutting  down.  This  practice  not  only  keeps  the  engine  in 
first-class  condition,  as  regards  cleanliness,  but  enables  the  opera- 
tor to  detect  the  first  indication  of  any  defect  that,  if  overlooked, 
might  result  seriously. 

II  a  knock  develops  in  a  steam  engine,  it  should  be  located  and 
remedied  at  once.  Knocking  is  usually  due  to  lost  motion  in 
bearings,  worn  journals,  or  cross-head  shoes,  water  in  the  cylinder, 


STEAM  ENGINES  133 

loose  piston,  or  to  poor  valve  setting.  Locating  knocks  in  steam 
engines  is  to  a  great  extent  a  matter  of  experience  and  no  definite 
rules  can  be  laid  down  which  will  meet  all  cases. 

However,  one  may,  by  careful  attention  to  the  machine,  learn 
to  trace  out  the  location  of  a  knock  in  a  comparatively  short 
time.  He  must  bear  in  mind  that  he  cannot  rely  on  his  ear  for 
locating  it,  as  the  sound  produced  by  a  knock  is,  in  many  cases, 
transmitted  along  the  moving  parts,  and  apparently  comes  from 
an  entirely  different  point. 

A  knock,  due  to  water  in  the  cylinder,  is  usually  sharp  and 
crackling  in  its  nature,  while  that  in  the  case  of  a  crank  or  a 
cross-head  pin  is  more  in  the  nature  of  a  thud.  If  the  knock 
should  be  due  to  looseness  of  the  main  bearings,  the  location  may 
be  detected  by  carefully  watching  the  flywheel.  If  the  cross- 
head  is  loose  in  the  guides  the  observer  may  be  able  to  detect 
a  motion  crossways  of  the  cross-head,  but  it  is  not  likely  that  he 
can  do  this  with  accuracy  in  the  case  of  a  high-speed  engine; in 
such  cases  the  cross-head  should  be  tested  when  the  engine  is  at 
rest.  No  adjustment  should  be  made  in  bearings  or  moving 
parts  of  an  engine  unless  the  machine  is  at  a  standstill  or  is  being 
turned  by  hand ;  never  when  under  its  own  power. 

The  heating  of  a  bearing  is  always  due  to  one  of  five  causes : 

1.  Insufficient  lubrication  due  to  insufficient  quantity  of  oil, 
wrong  kind  of  oil,  or  lack  of  proper  means  to  distribute  the  oil 
about  the  bearings. 

2.  The  presence  of  dirt  in  the  bearings. 

3.  Bearings  out  of  alignment. 

4.  Bearings  improperly  adjusted.  (They  may  be  either  too 
tight  or  too  loose.) 

5.  Operation  in  a  place  where  the  temperature  is  excessive. 
In  case  a  bearing  should  run  hot  and  it  is  very  undesirable  to 

shut  down,  it  is  generally  possible  to  keep  going  by  a  liberal 
application  of  cold  water  upon  the  entire  heated  surface  or  sur- 
faces. It  is  sometimes  possible  to  stop  heating  by  changing  from 
machine  oil  to  cylinder  oil  which  has  a  higher  flash  point. 

Should  a  bearing,  particularly  a  large  one,  be  over-heated  to 
the  extent  that  it  is  necessary  to  shut  down  the  engine,  do  not 
shut  down  suddenly  or  allow  the  bearing  to  stand  any  length  of 
time  without  attention.     This  is  particularly  important  in  the 


134       STEAM  AND  GAS  POWER  ENGINEERING 

case  of  babbitted  bearings,  as  the  softer  metal  of  the  bearings 
will  tend  to  become  brazed  to,  or  fused  with,  the  harder  metal  of 
the  shaft,  and  it  may  be  necessary  to  put  the  engine  through  the 
shop  before  it  can  be  used  again. 

In  case  of  the  necessity  of  shutting  down  for  a  hot  bearing, 
first  remove  the  load,  then  permit  the  engine  to  revolve  slowly 
under  its  own  steam  until  the  bearing  is  sufficiently  cool  to  per- 
mit the  bare  hand  to  rest  upon  it. 

The  presence  of  water  in  the  cylinder  is  always  a  source  of 
danger,  and  care  should  be  taken  that  the  water  of  condensation 
is  thoroughly  drained  from  the  cylinder  when  the  engine  is  first 
started,  at  shutting  down,  and  at  regular  intervals  throughout  the 
operation.  An  accumulation  of  water  may  readily  cause  the 
blowing  out  of  a  cylinder  head  with  its  resultant  loss  to  prop- 
erty and  possibly  to  life.  There  are  several  appliances  now  on 
the  market  which  automatically  safeguard  the  cylinder  head  by 
providing  a  weak  point  in  the  drain  system  which  will  relieve 
the  excess  pressure  before  the  cylinder  head  gives  way. 

Problems 

1.  Examine  the  power  plants  in  your  vicinity  and  report  upon  the  types 
of  valve  gears  used.  If  the  valve  mechanisms  in  any  case  differ  from  those 
in  this  text  book,  hand  in  clear  sketches  of  such  valve  gears. 

2.  Examine  the  locomotives  entering  your  city  and  report  upon  the  re- 
versing mechanisms  used. 

3.  Check  and  correct  the  valve  setting  of  some  engine,  accessible  to  you, 
and  report  upon  the  method  used. 

4.  Explain,  using  clear  sketches,  how  a  Corliss  engine  is  governed. 

5.  Calculate  the  indicated  horsepower  of  an  18"  X  24"  steam  engine 
operating  at  a  speed  of  110  revolutions  per  minute,  if  the  head-end  mean 
effective  pressure  is  30  pounds  per  square  inch,  the  crank-end  mean  effective 
pressure  30.5  pounds,  size  of  piston  rod  is  2  inches. 

6.  An  engine  operating  at  a  speed  of  200  revolutions  per  minute  is  tested 
by  means  of  a  Prony  brake.  If  the  length  of  the  brake  arm  is  42  inches  and 
the  net  weight  as  registered  on  platform  scales  35  pounds,  calculate  the  brake 
horsepower  of  the  engine. 

7.  Prepare  a  table  showing  economies  which  can  be  expected  at  full  load, 
half  load,  and  quarter  load,  from  the  following  types  of  engines : 

(a)  Simple  high-speed  automatic  engines,  sizes  50  to  150  horsepower. 

(b)  Corliss  engines,  simple  and  compound  non-condensing. 

(c)  Compound  condensing  engines  in  large  units. 

(d)  Uniflow  engines,  condensing  and  non-condensing. 


CHAPTER  VIII 


STEAM  TURBINES 


The  steam  turbine  differs  from  the  reciprocating  steam  engine, 
in  that  it  produces  rotary  motion  directly  and  without  any  re- 
ciprocating parts.  The  simple  steam  turbine  is  a  wheel  which 
is  given  rotary  motion  by  a  steam  jet  impinging  on  its  blades. 
The  elastic  force  of  the  steam  in  the  turbine  does  not  act  upon  the 
surface  of  a  moving  piston,  but  upon  the  mass  of  the  steam  itself, 
converting  nearly  all  of  the  available  energy  in  the  steam  between 
certain  pressure  limits,  into  velocity. 


sti> 


Fig.   109. — De  Laval  steam  turbine. 

In  one  type  of  steam  turbine,  (Fig.  109),  the  jet  of  steam  from 
a  fixed  expanding  nozzle  is  directed  upon  moving  curved  blades. 
All  the  expansion  occurs  in  a  nozzle,  resulting  in  a  steam  jet  of 
high  velocity  which  does  work.  This  is  called  the  impulse  type 
of  steam  turbine.  A,  B,  C,  and  D  are  stationary  expanding  noz- 
zles in  which  the  steam  is  completely  expanded  and  the  steam 
jet  of  high  velocity  strikes  the  blades  V,  giving  a  direct  rotary  mo- 
tion to  the  wheel  W  and  also  to  the  shaft  S. 

135 


136        STEAM  AND  GAS  POWER  ENGINEERING 

In  another  type,  called  the  reaction  turbine,  (Fig.  129),  the 
steam  is  expanded  within  the  stationary  and  the  moving  blades 
of  the  machine,  and  work  is  partly  produced  by  the  reaction  of 
the  expanding  steam  as  it  flows  from  the  moving  blades  to  the 
stationary  or  guide  blades.  No  commercial  steam  turbines 
operate  upon  the  pure  reaction  principle,  but  work  by  both  the 
impulse  of  the  steam  against  the  blades  and  by  the  reaction  of  the 
steam  as  it  leaves  the  blades. 

Advantages  of  the  Steam  Turbine. — As  compared  with  the 
reciprocating  engine  the  steam  turbine  has  the  following 
advantages: 

1.  The  speed  of  the  steam  turbine  is  practically  uniform. 
This  makes  the  steam  turbine  a  very  desirable  motor  for  electric 
central  stations. 

2.  The  steam  turbine  requires  no  internal  lubrication,  and  the 
exhaust  steam  may  be  used  again  without  oil  filtration. 

3.  The  steam  turbine  can  operate  at  lower  back  pressures, 
that  is  at  higher  vacua,  than  reciprocating  engines.  It  is  not 
practical  to  operate  steam  engines  at  vacua  greater  than  26 
inches.  Steam  turbines  are  commonly  operated  at  a  vacuum 
of  28  inches  and  some  turbine  installations  maintain  a  vacuum 
greater  than  29  inches.  Increasing  the  vacuum  from  26  to  29 
inches  increases  the  energy  of  the  steam  very  nearly  the  same 
amount  as  does  the  increase  in  steam  pressure  from  75  to  150 
pounds. 

4.  The  steam  turbine  is  better  adapted  to  use  highly  super- 
heated steam  than  are  reciprocating  engines  equipped  with 
slide  valves  or  with  Corliss  valves.  With  reciprocating  steam 
engines,  other  than  those  equipped  with  poppet  valves,  steam 
temperature  above  450°F.,  are  seldom  exceeded.  Above  such 
temperature  lubrication  is  unsatisfactory,  and  distortion  of  parts 
may  take  place.  Temperatures  of  600°F.  and  higher  are  common 
in  steam  turbine  practice. 

5.  The  steam  turbine  occupies  less  space  than  the  reciprocating 
engine  and  weighs  less  per  unit  capacity. 

6.  The  steam  turbine  can  be  built  in  very  large  sizes.  Recip- 
rocating engines  of  capacities  as  great  as  10,000  horsepower  are 
very  rare.  Steam  turbines,  each  of  which  has  a  capacity  of  30,000 
kilowatt  (over  40,000  horsepower)  and  greater,  are  found  in  large 


STEAM  TURBINES 


137 


generating  stations.  In  1918,  a  70,000  kilowatt  steam  turbine 
was  installed.  Other  steam  turbines  varying  in  capacity  from 
10,000  to  60,000  kilowatts  have  been  in  service  in  some  of  the  large 
central  stations  from  one  to  five  years,  operating  successfully 
from  16  to  20  hours  per  day. 

7.  Steam  turbines  in  large  sizes  are 
cheaper  than  reciprocating  engines. 

8.  Where  turbines  of  large  ca- 
pacities can  be  utilized,  electric  cur- 
rent can  be  generated  cheaper  than 
with  reciprocating  engines. 

History  of  the  Steam  Turbine. — 
The  history  of  the  steam  turbine 
dates  back  to  the  second  century 
before  the  birth  of  Christ,  when 
Hero  of  Alexandria  contrived  a  steam  motor  which  is  illus- 
trated in  Fig.  110.  The  Hero's  turbine  consisted  of  a  hollow 
spherical   vessel   rotating   on   two   supports.     The   steam   was 


Fig.  110. — Hero's  Turbine. 


Fig.  111. — Branca  Turbine. 


delivered  to  the  vessel  through  one  of  the  supports  M,  and  escaped 
from  it  through  two  bent  pipes  or  nozzles  N,  N  pointed  in  oppo- 
site directions.     Rotation  of  the  sphere  was  produced  by  the 


138        STEAM  AND  GAS  POWER  ENGINEERING 

reaction  due  to  the  steam  escaping  from  the  nozzles.  The  modern 
reaction  turbine  is  a  modification  of  the  Hero  motor. 

The  Branca  Wheel,  Fig.  Ill,  which  was  designed  in  1629, 
resembled  a  water  wheel,  and  was  driven  by  a  jet  of  steam  directed 
by  means  of  a  nozzle  upon  buckets  attached  to  the  wheel. 

The  steam  turbine  did  not  become  a  commercial  success 
until  near  the  end  of  the  nineteenth  century.  The  delay  in  the 
practical  utilization  of  the  turbine  was  due  to  the  following 
causes : 

1.  There  was  very  little  demand  for  a  high  speed  motor  of 
large  capacity  until  the  development  of  the  electric  central 
station. 

2.  Lack  of  scientific  knowledge  concerning  the  laws  governing 
the  flow  of  steam  has  prevented  the  perfection  of  a  machine 
which  could  operate  at  practical  speeds.  All  the  earlier  tur- 
bines were  single  stage  machines  and  operated  at  very  high 
speeds.  The  method  of  reducing  the  speed  of  the  turbine  shaft, 
by  passing  the  steam  through  a  number  of  wheels  in  series,  was 
not  discovered  until  about  the  middle  of  the  nineteenth  century. 

3.  The  simple  one  wheel  turbines,  of  which  the  Branca  tur- 
bine was  the  prototype,  could  not  be  built  as  commercial  motors 
until  the  developments  in  the  science  of  metallurgy  made  pos- 
sible the  manufacture  of  materials  which  were  capable  of  bearing 
without  rupture  the  high  rotative  speeds. 

The  De  Laval  Simple  Impulse  Steam  Turbine. — The  De  Laval 
steam  turbine  (Fig.  109)  was  the  first  successful  simple  impulse 
turbine.  The  inventor  of  this  turbine,  Dr.  Gustaf  de  Laval, 
designed  the  expanding  nozzle  in  1889.  He  also  patented  the 
principle  of  flexible  supports  for  turbines  or  other  bodies  intended 
to  rotate  at  high  velocities. 

Fig.  112  illustrates  a  sectional  plan  of  a  De  Laval  turbine. 
Steam  enters  the  steam  chest,  where  it  is  distributed  to  one  or  more 
nozzles,  depending  on  the  size,  is  expanded  to  the  exhaust  pres- 
sure, and  strikes  the  blades  on  the  turbine  wheel  C.  The  nozzles 
are  generally  fitted  with  stop  valves  by  which  one  or  more  nozzles 
can  be  cut  out  when  the  turbine  is  not  loaded  to  its  fullest  ca- 
pacity. The  turbine  wheel  C  is  mounted  on  a  flexible  shaft  D 
which  is  supported  at  the  bearings  K  and  7.  After  performing 
its  work,  the  steam  passes  into  the  chamber  W,  and  out  through 


STEAM  TURBINES 


139 


140        STEAM  AND  GAS  POWER  ENGINEERING 

the  exhaust  pipe  into  the  open  air  or  condenser.  Since  the  total 
expansion  of  the  steam  takes  place  in  one  set  of  nozzles,  the 
velocity  of  the  wheel  in  this  type  of  turbine  is  very  high,  and  this 
must  be  reduced  by  gearing.     The  turbine  shaft  D  is  connected 


Fig.   113. — Nozzles  for  a  De  Laval  turbine. 

to  the  pinion  which  engages  a  gear  wheel  M,  thus  reducing  the 
speed  of  the  shaft  Fto  that  required  by  the  machine  to  be  driven. 
A  throttling  governor  T  is  used  for  speed  regulation. 


Fig.  114. — Working  parts  of  a  De  Laval  steam  turbine. 

Different  nozzles  are  used  for  condensing  and  for  non-con- 
densing operation,  as  illustrated  in  Fig.  113.  The  difference  in 
the  taper  of  the  two  nozzles  shows  graphically  the  relative  ratios 
of  expansion   of   steam   when   expanding   against   atmospheric 


STEAM  TURBINES 


141 


pressure  or  into  a  vacuum.    A  is  the  steam  inlet  and  B  is  the 
outlet  from  the  nozzle. 

The  various  working  parts  of  a  De  Laval  turbine  are  illus- 
trated in  Fig.  114.  A  is  the  turbine  shaft,  B  is  the  turbine  wheel, 
C  is  the  pinion  which  meshes  with  the  gear  wheel  H  to  reduce  the 
speed  of  the  shaft  L.  M  is  a  coupling  which  connects  the  shaft 
J  to  the  machine  to  be  driven.  D,  E,  F,  G,  and  J  are  the  bearings 
for  supporting  the  pinion,  the  flexible  shaft,  and  the  gear  wheel 
respectively. 


Fig.  115. — De  Laval  governor. 


Fig.  115  shows  the  details  of  the  De  Laval  governor.  It 
consists  of  two  weights  D  which  are  pivoted  on  the  knife  edge 
with  hardened  pins  M  which  bear  upon  the  spring  seat  J. 
When  the  speed  exceeds  normal,  the  weights,  affected  by  centri- 
fugal force,  spread  apart,  pressing  on  the  spring  seat  J,  push 
the  governor  pin  I  to  the  right,  which  moves  with  it  the  bell 
crank  lever  L.  The  bell  crank  lever  L  operates  the  main  ad- 
mission valve,  throttling  the  steam  pressure. 

When  the  turbine  is  operated  condensing  and  overspeeds  the 
vacuum  valve  P  is  operated  by  the  governor  allowing  air  to 
enter  the  turbine  exhaust  pipe,  checking  the  turbine  speed. 


142       STEAM  AND  GAS  POWER  ENGINEERING 

Velocity  and  Energy  of  Steam. — The  velocity  of  steam  issuing 
from  a  nozzle  is  theoretically  produced  by  the  conversion  of 
heat  energy  into  kinetic  energy.  Steam  in  flowing  through  a 
nozzle  is  reduced  in  pressure,  and  the  resulting  expansion  releases 
heat  energy  which  is  utilized  in  accelerating  the  steam.  The 
velocit}"  resulting  when  steam  is  expanded  by  flowing  through  a 
perfect  nozzle  may  be  found  from  table  6. 

Table  6  has  been  calculated  by  determining  for  each  of  the 
various  pressures  the  total  available  energy  (E)  which  results 
when  steam  at  different  conditions  of  quality  (X)  or  of  superheats 
(S)  expands  in  a  perfect  nozzle.  Each  column  represents  the 
change  of  condition  which  results  when  steam  at  one  inlet  condi- 
tion is  expanded  through  the  nozzle.  Thus,  referring  to  column 
(1),  the  total  available  energy  at  two  different  pressures  repre- 
sents the  total  energy  before  and  after  the  expansion.  The  heat 
transformed  into  kinetic  energy  may  then  be  obtained  by  the 
differences.  Knowing  the  number  of  heat  units  available  for 
transformation,  the  resulting  velocity  may  be  read  directly  from 
the  scale. 

As  an  Illustration. — Steam  has  a  pressure  of  150  pounds  per 
square  inch  absolute,  and  is  superheated  128°F.  If  the  steam 
is  expanded  to  a  vacuum  of  28  inches,  or  1.0  pound  per  square 
inch  absolute,  what  will  be  the  velocity  of  the  steam  leaving  the 
nozzle? 

Solution. — Steam  superheated  128°F.  is  found  opposite  the 
pressure  of  150  pounds  per  square  inch  absolute  and  in  column  5, 
Table  6. 

The  total  heat  energy  of  the  steam  (E)  is  indicated  to  be 
1264  B.t.u.  To  find  the  exhaust  condition,  follow  down  column  5 
until  you  reach  the  total  energy  opposite  the  28  inch  vacuum 
pressure.  The  total  energy  (E)  for  this  condition  is  read,  922 
B.t.u. 

These  values  1264  and  922  represent  the  total  heat  energy  con- 
tained in  the  steam  before  and  after  the  expansion.  Conse- 
quently, the  available  heat  energy  utilized  in  creating  velocity 
is  obtained  by  subtracting  these  quantities. 

1264  -  922  =  342  B.t.u.  per  pound. 

From  the  velocity  scale,  in  connection  with  Table  6,  342  B.t.u. 


STEAM  TURBINES  143 

of  heat  per  pound  corresponds  to  a  velocity  of  4120  feet  per 
second. 

The  energy  developed  in  foot  pounds  by  the  steam  expanding 
in  a  nozzle  can  be  found  by  multiplying  778  by  the  available 
energy  E,  in  B.t.u.,  utilized  in  creating  velocity.  In  the  above 
problem,  the  energy  developed  by  one  pound  of  steam  in  expand- 
ing from  150  pounds  absolute  to  28  inches  vacuum  is  778  X 
342  =  266,076  foot  pounds. 

Compound  Impulse  Turbines. — From  the  example  in  the 
previous  section  it  is  evident  that  steam  attains  a  very  high 
velocity,  more  than  three-fourths  of  a  mile  per  second,  when  it 
expands  in  a  nozzle  between  a  pressure  of  150  pounds  absolute 
and  a  vacuum  of  28  inches.  To  utilize  efficiently  the  energy  of 
the  steam  in  a  turbine,  in  which  the  complete  expansion  of  the 
steam  occurs  in  one  set  of  nozzles  and  the  steam  at  high  velocity 
is  allowed  to  impinge  against  a  single  set  of  blades,  the  speed  of 
the  revolving  blades  should  approximately  equal  one-half  the 
velocity  of  the  steam.  A  turbine  operating  at  such  a  high  speed 
cannot  be  utilized  for  direct  connection  to  machines,  but  requires 
the  interposition  of  a  set  of  reducing  gears. 

The  various  compound  turbines  have  been  perfected  in  order 
to  do  away  with  the  reduction  gearing  of  the  simple  impulse 
types.  In  the  simple  impulse  turbine  the  complete  expansion  of 
the  steam  from  boiler  pressure  to  exhaust  pressure  takes  place 
in  one  set  of  nozzles  and  the  velocity  acquired  in  the  nozzles  is 
given  up  to  a  single  revolving  wheel.  In  one  type  of  compound 
impulse  turbines  the  expansion  of  the  steam  takes  place  in  a  series 
of  steps  or  stages,  each  stage  being  provided  with  a  set  of  nozzles 
and  a  single  revolving  wheel.  In  another  type,  the  speed  is 
reduced  by  giving  up  the  energy  of  the  steam  to  several  revolv- 
ing wheels,  the  direction  of  the  steam  between  the  wheels  being 
changed  by  stationary  blades. 

The  Rateau  Turbine. — The  Rateau  turbine,  Fig.  116,  consists 
of  a  number  of  stages,  each  stage  including  one  row  of  moving 
blades  and  a  set  of  stationary  nozzles.  The  steam  enters  through 
the  first  set  of  stationary  nozzles,  in  which  it  expands  to  a  lower 
pressure  with  a  corresponding  increase  in  velocity,  and  strikes 
the  first  set  of  revolving  blades.  The  steam  next  passes  through 
the  second  set  of  stationary  nozzles,  which  are  of  greater  area 


144       STEAM  AND  GAS  POWER  ENGINEERING 


Table  6. — Guide  for  Determining  Velocities  Resulting  from  Expand- 
ing Steam  in  a  Perfect  Nozzle 


Pressure,  lb.  per  sq.  in. 

Total  energy  "£," 

and  quality 

Gage 

Absolute 

1 

2 

3 

4 

5 

235 

250.0 

£  =  1135 

£  =  1178 

£  =  1220 

£  =  1266 

£  =  1318 

X  =  0.920 

X  =  0.971 

S  =  25° 

5  =  107° 

S  =  206° 

185 

200.0 

£  =  1118 

£  =  1160 

£  =  1201 

£  =  1240 

£  =  1294 

X  =  0.905 

X  =  0.955 

S  =  5° 

S  =  78° 

S  =  172° 

135 

150.0 

£  =  1096 

£  =  1137 

£  =  1178 

£  =  1219 

£  =  1264 

X  =  0.887 

X  =  0.935 

X  =0.982 

5  =  42° 

S  =  128° 

110 

125.0 

£  =  1082 

£=1122 

£  =  1161 

£  =  1203 

£=1246 

X  =  0.877 

X  =  0.922 

X  =  0.969 

5  =  22° 

S=102° 

85 

100.0 

£  =  1066 

£  =  1106 

£  =  1145 

£  =  1185 

£  =  1225 

X  =  0.865 

X  =  0.91 

X  =  0.954 

X  =  0.998 

S  =  72° 

65 

80.0 

£  =  1051 

£  =  1090 

£  =  1128 

£  =  1166 

£=1206 

X  =  0.855 

X  =  0.898 

X  =  0.940 

X  =  0.982 

S  =  45° 

45 

60.0 

£=1031 

£  =  1069 

£  =  1106 

£  =  1145 

£  =  1182 

X  =0.842 

X  =  0.883 

X  =  0.924 

X=  0.965 

5=10° 

15 

30.0 

£  =  987 

£  =  1023 

£=1058 

£  =  1094 

£  =  1129 

X  =  0.814 

X  =  0.851 

X  =  0.888 

X  =  0.926 

X  =  0.964 

atmospheric 

0 

15.0 

£  =  946 

£  =  979 

£  =  1013 

£  =  1043 

£  =  1080 

X  =0.790 

X  =  0.823 

X  =  0.858 

X  =  0.893 

X  =  0.928 

in.  mercury 

vacuum 

10 

10.0 

£  =  923 

£  =  955 

£  =  988 

£  =  1020 

£=1053 

X  =  0.776 

X  =  0.809 

X  =  0.842 

X  =  0.876 

X  =  0.908 

20 

5.0 

£  =  886 

£  =  916 

£  =  948 

£  =  979 

£  =  1010 

X  =  0.756 

AT  =  0.786 

X  =  0.818 

X  =  0.849 

X  =  0.880 

24 

3.0 

£  =  860 

£  =  890 

£  =  921 

£  =  950 

£  =  980 

X  =  0.742 

X  =0.772 

X  =  0.802 

X  =0.831 

X  =  0.861 

26 

2.0 

£  =  840 

£  =  870 

£  =  899 

£  =  928 

£  =  958 

X=0.731 

X  =0.760 

X  =  0.789 

X=0.818 

X  =  0.847 

28 

1.0 

£  =  810 

£  =  837 

£  =  865 

£  =  894 

£  =  922 

X  =  0.716 

X  =0.742 

X  =  0.769 

X  =  0.797 

X  =0.823 

29 

0.5 

£  =  806 
X  =  0.726 

£  =  833 
X=0.751 

£  =  860 
X  =  0.777 

£  =  888 

X  =  0 . 802 

STEAM  TURBINES 


145 


"A"'  or  superheat  "<S" 

>»  ,: 

«i 

•£•     M 

D\ 

14. 

Sm 

6 

7 

8 

9 

10 

^£ 

ti 

o — 

;^6C0 

=-1000 

— 

=^5- 



^^1500 

— 

50— 

#  =  1314 

ii-2000 

■= 

5  =  230° 

|=§ff" 

100-^ 

#=1294 

=- 

J-* 

5  =  198° 

Hf-2500 

-E 

#  =  1270 

=~ 

150 -^ 

5  =  162° 

HJi- 

_Z 

#=1244 

#  =  1297 

=-3000 

~ 

S  =  129° 

5  =  228° 

JJS. 

200-^ 

#  =  1222 

#  =  1266 

H- 

— 

5  =  68° 

5  =  180° 

=-3500 

250— 

#  =  1164 

#  =  1 202 

:== 

X  =  1.00 

S  =  60° 

= 

— 

#  =  1114 

#  =  1148 

#  =  1221 

:E=_ 

~ 

X  =  0.963 

X  =  0.997 

5  =  100° 

^4000 

300-5 

#=1186 

#  =  1118 

#  =  1186 

EEL 

~ 

X  =  0.943 

X  =  0.975 

S  =  94° 

S- 

350-^ 

#  =  1041 

#  =  1172 

#  =  1134 

#  =  1168 

=- 

_Z 

Z  =  0.911 

X  =  0.942 

S  =  9° 

5  =  82° 

= 

~ 

#=1010 

#  =  1040 

#  =  1100 

#  =  1130 

j=-4500 

400-5 

Z  =  0.890 

X  =  0.920 

X  =  0.979 

5  =  20° 

~z 

z 

#  =  987 

#  =  1015 

#  =  1075 

#  =  1105 

#  =  1036 

= 

"5 

X  =  0.875 

X  =  0.913 

X  =  0.961 

AT  =  0.990 

S  =  45° 

== 

450~5 

#  =  950 

#  =  978 

#  =  1034 

#  =  1062 

#=1090 

==" 

_n 

X  =  0.851 

X  =  0.878 

X=  0.932 

X  =  0.959 

X  =  0.987 

EEr- 

■Jj 

#  =  914 

#=941 

#=995 

#  =  1022 

#  =  1049 

EEl5000 

500^ 

A*  =  0.828 

X  =  0.854 

X  =  0.905 

Z  =  0.931 

X  =  0.957 

Velocity 
Scale 

10 


146        STEAM  AND  GAS  POWER  ENGINEERING 


than  the  first,  because  the  volume  of  steam  was  increased  by  its 
expansion  in  the  first  set.     Here  the  steam  again  expands  and 


enters  the  second  row  of  moving  blades,  and  the  process  is  repeated 
in  succeeding  stages  until  the  steam  reaches  the  exhaust  outlet. 


STEAM  TURBINES 


147 


The  Kerr  Turbine. — The  Kerr  steam  turbine,  illustrated  in 
Fig.  117,  is  similar  to  the  Rateau  in  that  the  expansion  of  the 
steam  takes  place  in  a  series  of  stages,  each  stage  being  provided 


Fig.  117. — Kerr  steam  turbine. 

with  a  set  of  nozzles  and  a  single  revolving  wheel.  The  expan- 
sion in  a  Kerr  turbine  is  carried  out  in  from  six  to  ten  stages. 
The  steam  is  partly  expanded  in  the  first  set  of  nozzles,  and  the 
energy  developed  is  abstracted  by  the  first  revolving  wheel. 
The  steam  then  expands  in  a  second  and  subsequent  set  of  nozzles 
until  the  steam  from  the  last  revolving  wheel  enters  the  exhaust. 

A  single  stage  simple  impulse 
turbine  with  double  cup-shaped 
blades  is  illustrated  in  Fig.  118. 
This  type  of  turbine  was  formerly 
manufactured  by  the  Kerr  Com- 
pany. 

The  Kerr  steam  turbine  is  gov- 
erned by  a  centrifugal  spring-loaded 
throttling  governor  mounted  directly 
on  the  turbine  shaft,  and  acting 
through  suitable  connections  upon 
the  steam  valve  stem.  An  emergency  governor,  entirely  inde- 
pendent of  the  main  governor,  shuts  down  the  turbine,  when  it 
overspeeds,  by  closing  a  valve  in  the  steam  line. 


Fig.   118.— Turbine    with 
double  cup-shaped  blades. 


148       STEAM  AND  GAS  POWER  ENGINEERING 

De  Laval  Multiple  Impulse  Turbine.- — The  De  Laval  multiple 
impulse  turbine  is  illustrated  in  Fig.  119.  It  consists  of  a  series 
of  blade  wheels  which  revolve  in  independent  chambers  formed 
between  diaphragms  held  in  the  casing  of  the  turbine.  Steam 
is  admitted  to  the  steam  chest  at  the  right  hand  end  of  the  tur- 
bine and  is  directed  by  means  of  nozzles  upon  the  blades  of 
the  first  revolving  wheel.  The  steam  leaving  the  first  revolving 
wheel  passes  through  guide  blades,  which  are  set  around  the 


Fig.  119. — De  Laval  multiple-impulse  steam  turbine. 

entire  periphery  of  the  diaphragm  separating  the  first  and  second 
stages,  and  strikes  the  blades  of  the  second  revolving  wheel,  and 
so  on  through  the  succeeding  stationary  and  revolving  blades. 

The  governing  of  the  De  Laval  Multiple  impulse  turbine  is 
accomplished  by  throttling  the  admission  of  the  steam  to  the 
steam  chest.  An  emergency  governor  is  mounted  in  the  end  of 
the  turbine  shaft,  entirely  independent  of  the  main  speed  gover- 
nor, and  can  be  adjusted  to  act  at  any  predetermined  speed. 

De  Laval  multiple  impulse  machines  are  provided  with  reduc- 
tion gears  for  the  driving  of  machines  at  slow  speeds. 


STEAM  TURBINES 


149 


The  Terry  Turbine. — The  principle  Gf  the  Terry  turbine  is 
illustrated  in  Fig.  120.  This  turbine  consists  of  one  set  of  nozzles 
and  one  revolving  wheeL    The  steam  is  expanded  in  the  nozzle 


Section  Thrud-A  ' 
Fig.   120. — Terry  steam  turbine. 

from  approximately  boiler  pressure  to  exhaust  pressure.  The 
jet  of  steam  issuing  from  the  nozzle  N,  at  high  velocity, 
strikes  the  side  of  the  wheel  blades,  is  reversed  in  direction 


Fig.  121. — Parts  of  a  Sturtevant  turbine. 


180  degrees,  and  is  guided  into  one  of  the  stationary  reversing 
blades  R,  by  means  of  which  the  jet  is  redirected  a  second  time 
on  the  buckets  B  of  the  wheel.    This  process  is  repeated  several 


150        STEAM  AND  GAS  POWER  ENGINEERING 

times  until  all  the  available  energy  of  the  steam  has  been  ab- 
stracted by  the  revolving  element. 

The  Sturtevant  Turbine. — The  Sturtevant  turbine  (Fig.  121) 
is  similar  to  the  Terry  turbine  in  that  the  steam  from  the  moving 
blades  is  diverted  back  into  the  stationary  blades  next  to  the 
nozzle.  A  sectional  view  through  a  Sturtevant  turbine  is  shown 
in  Fig.  122.  A  throttling  governor  is  used  to  regulate  the  speed 
of  this  turbine. 


Fig.  122. — Sectional  view  of  a  Sturtevant  turbine. 


The  Westinghouse  Impulse  Turbine. — The  Westinghouse 
impulse  turbine  operates  on  the  same  principle  as  the  Sturte- 
vant and  Terry  turbines. 

The  Curtis  Steam  Turbine. — In  the  Curtis  steam  turbine, 
the  expansion  of  the  steam  takes  place  in  several  stages  and  the 
velocity  acquired  in  the  nozzles  of  each  stage  is  abstracted  by 
one  or  two  revolving  wheels.  The  number  of  stages  varies 
from  four  to  nine  or  more,  depending  upon  the  size  of  the  machine. 
In  very  small  sizes  the  Curtis  turbine  is  built  as  a  one  stage 
machine,  with  two  or  three  revolving  wheels. 


STEAM  TURBINES 


151 


The  action  of  the  Curtis  turbine  is  illustrated  by  Fig.  123. 
Steam  at  boiler  pressure  enters  through  one  or  more  admission 
valves  B  into  the  steam  chest  C.     The  steam  from  the  steam  chest 


Fig.  123. — Arrangement  of  nozzles  and  blades  in  two-slage  Curtis  steam  turbine. 

enters  the  expanding  nozzles  D.  The  number  of  admission 
valves  used  is  controlled  by  the  governor  in  accordance  with  the 
load.     The  steam  jet  at  high  velocity  issuing  from  the  nozzle  D 


Fig.  124. — First  stage  nozzle  plate  for  a  Curtis  turbine. 

strikes  the  moving  blades  F}  giving  up  a  portion  of  its  energy. 
The  direction  of  the  steam  is  changed  by  the  stationary  or  guide 
blades  G,  called  intermediates,  striking  the  second  set  of  moving 


152        STEAM  AND  GAS  POWER  ENGINEERING 

blades  H.  The  steam  issuing  from  the  second  set  of  moving 
blades  enters  the  second  stage,  where  it  is  further  expanded  by 
means  of  nozzles  K  and  the  energy  developed  is  abstracted  by 


Fig.  125. — Blading  of  Curtis  turbine. 


\_J 

avS 

JU"3 

M  i 

,,„„.     _   :    . 

r     ■ \             x     ** 

!   v               Y     1 

7TT% 

**rr 

^T     =&?      ' 

Fig.  126. — Horizontal  Curtis  steam  turbine. 

moving  blades  M.     The  same  operation  is  repeated  in  the  third 
and  in  the  subsequent  stages. 

The  expanding  nozzles  of  the  first  stage  of  a  Curtis  turbine 


STEAM  TURBINES 


153 


are  illustrated  in  Fig.  124.  These  extend  around  a  relatively 
short  arc  of  the  periphery  in  the  first  stage,  while  in  the  low 
pressure  end  they  extend  around  the  entire  wheel. 


Fig.   127. — Vertical  Curtis  steam  turbine. 


The  method  used  in  fastening  blades  of  a  Curtis  turbine  is 
illustrated  in  Fig.  125. 

The  Curtis  turbine  is  constructed  as  a  horizontal  machine 


154       STEAM  AND  GAS  POWER  ENGINEERING 

(Fig.  126).  The  vertical  arrangement  (Fig.  127),  used  in  some 
of  the  earlier  designs,  is  now  obsolete,  but  units  of  this  type 
can  still  be  found  in  operation  in  many  of  the  large  power 
plants.  In  the  vertical  turbines  the  shaft  is  supported  by  a 
step-bearing  at  the  lower  end.  Oil  is  pumped  under  this  bear- 
ing at  considerable  pressure,  thus  floating  the  entire  revolving 
element  on  an  oil  film. 

Small  Curtis  turbines  are  controlled  by  means  of  a  throttling 
governor.  Large  turbines  are  controlled  by  an  indirect  type 
of  governor,  which  mechanically  or  through  a  pilot  valve  and 


Fig.  128. — Hydraulic  governor  for  Curtis  turbine. 

a  hydraulic  cylinder  opens  or  closes  the  admission  valves,  thus 
regulating,  in  accordance  with  the  load,  the  number  of  nozzles 
which  are  open  for  the  discharge  of  steam.  The  hydraulic  type 
of  governor  for  Curtis  turbines  is  illustrated  in  Fig.  128. 

Curtis  turbines  are  equipped  with  an  automatic  emergency 
governor,  independent  of  the  main  governor,  which  through  a 
trip  operates  the  main  throttle  valve  when  the  turbine  speed 
exceeds  a  predetermined  limit. 

The  Reaction  Turbine. — The  reaction  steam  turbine  differs 
from  the  impulse  turbines  in  that  stationary  blades  are  substi- 
tuted for  nozzles.     The  blades  are  shaped  so  that  they  can  per- 


STEAM  TURBINES 


155 


form  the  functions  of  the  nozzles  and  of  the  blades  of  impulse 
turbines.  The  reaction  turbine  has  many  stages,  each  stage 
consisting  of  a  set  of  stationary  and  of  rotating  blades.  Part 
of  the  expansion  of  the  steam  takes  place  in  the  stationary  blades 
and  part  in  the  moving  blades.  In  the  impulse  turbine  the  pressure 
on  both  sides  of  the  moving  wheel  is  very  nearly  the  same;  in  the 
reaction  turbine  the  pressure  at  the  inlet  to  the  wheel  blade  is 
greater  than  the  pressure  at  the  outlet. 

The    Parsons    Turbine. — The    principle    of   the    single   flow 
Parsons  reaction  turbine  is  illustrated  in  Fig.  129. 


Fig.  129. — Sectional  view  of  a  Parsons  turbine. 


The  steam  enters  a  governor  valve,  reaches  the  chamber  I 
and  passes  out  to  the  right  through  the  turbine  blades,  eventually 
arriving  at  the  exhaust  chamber  E.  The  areas  of  the  passages 
increase  progressively  in  volume,  corresponding  with  the  expan- 
sion of  the  steam. 

The  rotating  part  of  the  turbine  consists  of  a  long  drum  upon 
which  are  mounted  the  moving  blades.  The  stationary  or  guide 
blades  are  fitted  in  rings  fastened  to  the  turbine  casing. 

On  the  left  of  the  steam  inlet  are  shown  the  revolving  balancing 
pistons,  one  corresponding  to  each  cylinder  or  section  of  the 
turbine.     The  steam  at  /  presses  against  the  turbine  and  goes 


156        STEAM  AND  GAS  POWER  ENGINEERING 


through  doing  work.  It  also  presses  in  the  reverse  direction, 
but  cannot  pass  the  piston,  thus  equalizing  the  pressure  and 
reducing  end  thrust  on  the  shaft.  In  most  designs  of  Parsons 
turbines  all  the  balancing  pistons  are  at  the  pressure  end  of 
the  turbine.  In  the  Allis-Chalmers  Parsons  turbine  the  largest 
balancing  piston  is  placed  at  the  low  pressure  end  of  the  rotating 
element  behind  the  last  row  of  blades. 

At  T  is  shown  a  thrust  bearing  which  serves  to  maintain  the 
correct  adjustment  of  the  balancing  pistons.  Q  is  a  pipe  con- 
necting the  back  of  the  balancing  piston  at  S  with  the  exhaust 
chamber  E',  to  insure  that  the  pressure  at  this  point  should  be  the 
same  as  that  of  the  exhaust.  The  governor  gear  and  oil  pumps 
generally  receive  their  motion  by  means  of  a  worm  wheel,  gearing 
into  a  worm  cut  on  the  outside  of  the  coupling.  An  oil  reservoir 
is  provided  into  which  drains  all  the  oil  from  the  bearings.  From 
there  it  flows  to  a  pump  to  be  pumped  to  a  chamber,  where 
it  forms  a  static  head  which  gives  a  continuous  pressure  of  oil  to 
the  bearings.  A  by-pass  valve  is  provided,  this  valve  admit- 
ting high-pressure  steam  to  the  lower  stages.     By  opening  this 

valve  the  turbine  can  carry 
considerable  overload  or  to 
operate  non-condensing  at 
nearly  full  load. 

Reaction  turbines  are 
controlled  by  an  indirect 
type  of  governor,  which 
causes  the  main  steam  ad- 
mission valve  to  remain 
open  for  longer  or  shorter 
periods  of  time,  depending 
upon  the  load  carried  by  the  machine.  The  governor  is  of  the 
fly  ball  type  and  is  illustrated  diagrammatically  in  Fig.  130. 

The  governor  levers  (Fig.  130)  are  attached  to  the  small  relay 
valve  which  operates  the  main  admission  valve.  The  levers  receive 
reciprocating  motion  at  C  from  an  eccentric  and  use  the  governor 
clutch  as  a  fulcrum,  points  D  and  E  being  fixed.  Continuous 
reciprocating  motion  is  thus  given  to  the  relay  valve.  This  is  in 
turn  transmitted  to  the  admission  valve.  The  function  of  the 
governor  is  to  vary  the  plane  of  oscillation  of  the  relay  valve, 


Fig.   130. — Governor  for  Parsons  turbine. 


STEAM  TURBINES 


157 


which  causes  the  admission  valve  to  remain  open  for  a  longer 
or  shorter  period,  according  to  the  position  of  the  governor. 


1 

*mH 

1 

""'^^^SfiNfcv     ^"        '~*    H  '/ 

■P^a                      ' '  [ 

Fig.   131. —  Westinghouse-Parsons  turbine  with  the  upper  casing  removed. 


Fia.  132. — Blading  of  Westinghouse-Parsons  turbines. 

Thus  the  steam  is  admitted  in  puffs,  which  occur  at  constant 
intervals  of  time.     The  puffs  are  either  of  long  or  short  duration 


158        STEAM  AND  GAS  POWER  ENGINEERING 

according  to  the  load.  At  heavy  loads  the  puffs  merge  in  a  con- 
tinuous blast.  With  this  type  of  governor  high-pressure  steam 
is  used  at  all  loads. 

A  Westinghouse-Parsons  turbine  with  its  upper  casing  re- 
moved is  illustrated  in  Fig.  131.  The  method  used  in  fastening 
the  blades  of  a  Westinghouse-Parsons  steam  turbine  is  illus- 
trated in  Fig.  132. 

The  Impulse-reaction  Turbine. — A  section  through  a  com- 
bined impulse  and  reaction  turbine  is  shown  in  Fig.  133.     The 


WW  t**^ 


Fig.  133. — Double-flow  Westinghouse  turbine. 

impulse  element  is  similar  to  the  first  stage  of  a  Curtis  turbine, 
and  consists  of  one  set  of  nozzles,  an  impulse  wheel  with  two 
rows  of  revolving  blades,  and  a  set  of  stationary  blades.  Steam 
first  enters  the  turbine  nozzles,  is  partly  expanded,  and  impinges 
upon  the  impulse  blades.  The  remaining  energy  of  the  steam 
after  leaving  the  impulse  blades  is  utilized  in  the  reaction  element 
of  the  turbine. 

The  impulse-reaction  turbine  occupies  less  space  than  the 
pure  reaction  machine.  It  is  constructed  either  as  a  single  flow  or 
as  a  double  flow  machine.     In  the  single  flow  the  reaction  elements 


STEAM  TURBINES 


159 


are  on  one  side  of  the  impulse  stage,  while  in  the  double  flow 
(Fig.  133)  the  reaction  elements  are  on  both  sides  of  the  impulse 
wheel. 

The  Spiro  Steam  Turbine. — The  Spiro  steam  turbine,  which 


Fig.   134. — Rotors  of  the  Spiro  turbine. 


is  illustrated  in  Figs.  134  and  135,  consists  of  two  herringbone 
gears  in  mesh  which  revolve  in  a  close-fitting  casing.  Steam  is 
admitted  at  mid-length  into  the  tooth  pockets  at  the  point  A  of 
each  rotor.     As  the  rotor  turns,  the  tooth  space  occupied  by  the 


Fig.  135. — Casing  or  cylinder  of  the  Spiro  turbine. 


steam  increases  in  length  and  the  steam  expands.  The  steam 
escapes  when  the  outer  ends  of  the  teeth  pass  the  line  of  contact 
between  the  two  rotors.  The  inlet  port  openings  are  situated 
one  on  each  side  of  the  central  rib,  as  illustrated  in  Fig.  135. 
This  turbine  is  governed  by  throttling  the  steam. 


160        STEAM  AND  GAS  POWER  ENGINEERING 

The  Spiro  steam  turbine  is  not  suitable  for  condensing  opera- 
tion, but  is  compact  and  is  used  for  the  driving  of  pumps,  fans, 
and  other  auxiliaries  in  connection  with  power  plants,  office 
buildings,  and  factories. 

Exhaust  Steam  Turbines. — A  steam  turbine  installed  between 
the  exhaust  of  a  reciprocating  engine  and  a  condenser  is  called 
an  exhaust  steam  turbine.  The  reciprocating  steam  engine  does 
not  show  as  high  an  economy  at  high  vacuum  as  does  the  steam 
turbine.  The  capacity  and  economy  of  reciprocating  engine 
steam  power  plants  have  been  increased  by  the  addition  of  a  low 
pressure  turbine. 

Exhaust  steam  turbines  may  be  operated  as  straight  low  pres- 
sure turbines  using  only  exhaust  steam  from  engines,  or  as 
mixed  pressure  turbines  which  operate  on  high  and  low  pressure 
steam  at  the  same  time. 

Ordinarily,  combined  reciprocating  engines  and  low  pressure 
steam  turbines  would  not  be  selected  for  a  new  installation,  as 
the  cost  of  the  combined  units  is  much  greater  than  that  of  the 
high  pressure  steam  turbine.  The  field  of  the  low  pressure  steam 
turbine  is  in  connection  with  the  large  non-condensing  reciprocat- 
ing engine  power  plant. 

Applications  of  the  Steam  Turbine. — The  steam  turbine  is 
applicable  to  work  which  requires  a  high  and  constant  rotative 
speed,  where  a  high  starting  effort  is  not  required,  and  where 
there  is  no  need  of  reversing  the  direction  of  motion.  These 
conditions  exist  in  electric  generating  stations.  For  service  in 
which  the  speed  is  low  and  variable,  where  a  reversal  of  direction 
is  necessary,  or  where  the  starting  torque  is  high,  the  turbine  is 
unsuited  and  the  reciprocating  engine  is  better  adapted.  Speed- 
reduction  and  reversing  gears  have  been  employed  in  connection 
with  turbines,  but  these  have  only  a  limited  application. 

The  steam  turbine  is  very  seldom  operated  non-condensing; 
in  power  plants  where  the  exhaust  steam  is  used  for  heating  or 
for  manufacturing  purposes  the  reciprocating  engine  will 
usually  be  found  more  satisfactory. 

Steam  turbines  are  used  to  some  extent  for  the  driving  of  power 
plant  auxiliaries,  such  as  boiler  feed  pumps,  hot  well  pumps  and 
circulating  pumps;  also  high  pressure  fans  and  blowers. 

Steam  turbines  are  also  employed  for  the  propulsion  of  ships. 


STEAM  TURBINES  161 

The  steam  turbine  has  less  weight  and  requires  less  space  than 
the  reciprocating  engine  of  the  same  size.  Vessels  propelled 
by  steam  turbines  are  more  stable  on  account  of  the  lower  center 
of  gravity  of  the  machinery.  The  steam  turbines  are  usually 
connected  to  the  propellers  by  means  of  gears.  In  some  cases  the 
steam  turbine  drives  an  electric  generator  and  the  propellers  are 
driven  by  electric  motors,  which  receive  their  current  from  the 
generator  of  the  turbine. 

Steam  Turbine  Economy. — The  economy  of  steam  turbines 
is  usually  expressed  in  pounds  of  steam  per  kilowatt  hour, 
as  the  greatest  field  of  the  turbine  is  for  the  driving  of  electric 
generators.  Steam  turbines  in  sizes  of  1,000  to  10,000  kilowatt, 
when  operated  at  150  to  200  pounds  gage  pressure,  with  super- 
heats of  100°  to  200°F.  and  with  a  vacuum  of  28  to  29  inches, 
will  develop  a  kilowatt  on  12  to  15  pounds  of  steam  per  hour. 
Better  economies  are  secured  as  the  size  of  the  unit  increases. 
The  smaller  condensing  steam  turbines,  when  operated  with 
saturated  steam,  will  consume  18  to  30  pounds  of  steam  per  kilo- 
watt per  hour.  Steam  turbines  when  operated  non-condensing 
will  consume  50  to  75  pounds  of  steam  per  kilowatt  per  hour. 

Steam  turbines  under  ordinary  operating  conditions  will  show 
a  gain  of  about  8  per  cent,  for  each  100  degrees  superheat.  The 
presence  of  moisture  will  decrease  the  economy  or  increase  the 
steam  consumption  by  about  2  per  cent,  for  1  per  cent,  of  mois- 
ture in  the  steam.  Increasing  the  vacuum  from  27  to  28  inches 
will  increase  the  turbine  economy  from  3.0  to  5  per  cent.  In- 
creasing the  steam  pressure  from  150  to  200  pounds  will  increase 
the  economy  about  3  per  cent. 

Installation  and  Care  of  Steam  Turbines. — The  general  rules 
given  in  Chapter  Vll  concerning  the  installation  and  care  of 
reciprocating  steam  engines  apply  also  to  steam  turbines. 

The  steam  turbine  should  be  located  so  that  it  will  be  acces- 
sible from  all  sides  for  inspection  and  repair.  Proper  crane  and 
hoist  facilities  should  be  available  for  all  parts  which  are  too 
heavy  to  be  handled  by  hand. 

The  foundation  should  be  sufficiently  heavy  to  afford  a  per- 
manent support  and  rigid  enough  to  prevent  springing  or 
warping  any  part  of  the  turbine.  To  prevent  vibrations  from 
being  conducted  to  the  building,  a  space  should  always  be  left 
li 


162        STEAM  AND  GAS  POWER  ENGINEERING 

between  the  turbine  foundation  and  the  walls  or  floors;  this 
space  should  be  filled  with  some  soft  material.  After  the  founda- 
tion is  properly  set,  care  must  be  taken  to  obtain  proper  adjust- 
ment of  the  turbine.  Small  steam  turbines  are  usually  placed  on 
concrete  floors  without  foundations. 

The  piping  must  be  so  designed  and  installed  that  no  strain 
will  be  thrown  on  the  turbine  due  to  expansion  and  contraction, 
or  on  account  of  the  piping  being  improperly  supported.  Water 
pockets  in  the  piping  should  be  avoided. 

Before  starting  a  steam  turbine  for  the  first  time,  care  must  be 
taken  to  blow  out  the  steam  and  oil  from  the  piping  in  order  to 
remove  scale  and  dirt.  The  oiling  system  should  then  be  put 
in  operation  and  the  turbine  should  be  warmed  up  and  started 
slowly,  listening  for  any  clicking  or  rubbing  sounds,  which  may 
require  investigation.  While  the  turbine  is  turning  over  slowly 
the  oiling  system  and  the  auxiliaries  should  be  examined. 
Heating  of  the  bearings  may  be  due  to  grit  or  to  poor  alignment. 
After  ascertaining  that  everything  is  in  good  working  order,  the 
turbine  should  gradually  be  brought  up  to  speed.  As  the  tur- 
bine approaches  full  speed,  the  action  of  the  governor  should  be 
observed.  If  the  governor  is  working  properly,  the  turbine  is 
ready  for  the  load. 

In  starting  a  condensing  turbine,  the  condenser  auxiliaries 
are  started  first,  and  after  the  vacuum  has  been  obtained,  the 
turbine  is  started. 

Problems 

1.  To  gain  a  conception  as  to  the  enormous  amount  of  power  a  70,000 
kilowatt  turbine  develops,  calculate  the  following: 

(a)  If  all  the  energy  of  a  70,000  kilowatt  turbine  is  used  to  supply  light, 
calculate  the  number  of  candle  power  it  will  supply  by  means  of  Tungsten 
lamps. 

(b)  If  a  70,000  kilowatt  turbine  develops  a  kilowatt  on  2}4  pounds  of 
coal  per  hour,  calculate  the  amount  of  fuel  required  to  keep  such  a  turbine 
in  operation  at  full  load  for  ten  hours. 

2.  Calculate,  using  Table  6,  the  energy  in  foot  pounds  which  will  be 
developed  when  steam,  initially  2  per  cent,  wet,  expands  in  a  perfect  nozzle: 

(a)  From  150  pounds  absolute  to  atmospheric, 

(6)  From  150  pounds  absolute  to  28  inches  vacuum. 

3.  Calculate  and  compare  the  velocities  developed  by: 
(a)  Water  falling  through  a  head  of  200  feet. 


STEAM  TURBINES  163 

(b)  Steam,    initially   dry,    expanding  in   a  perfect  nozzle  from  a  steam 
pressure  of  200  pounds  absolute  to  a  vacuum  of  29  inches. 

4.  Show  by  means  of  clear  sketches  the  details  of  governors  used  in 
connection  with: 

(a)  Simple  impulse  turbines, 
(6)  Curtis  turbines, 

(c)  Parsons  turbines. 

6.  Explain  how  vessels  propelled  by  steam  turbines  are  reversed. 


CHAPTER  IX 

ENGINE  AND  TURBINE  AUXILIARIES 

Many  of  the  auxiliaries  which  properly  belong  to  the  engine 
and  turbine  have  been  described  in  Chapters  IV,  V,  VI,  VII, 
and  VIII.  This  chapter  will  deal  mainly  with  condensers  and 
condenser  auxiliaries,  but  will  include  other  apparatus  which 
can  be  called  auxiliaries  or  accessories  to  an  engine  or  turbine. 

Condensers 

The  Principle  of  the  Condenser. — The  advantage  gained  by 
operating  a  steam  engine  condensing  is  due  to  the  reduction  in 
the  back  pressure  against  which  the  engine  exhausts.  In  the 
case  of  the  steam  turbine,  the  available  energy  in  the  steam  can 
be  more  than  doubled  by  carrying  high  vacua,  as  compared 
with  non-condensing  operation. 

The  gain  in  economy  which  can  be  expected  by  increasing  the 
vacuum  depends  to  some  extent  upon  the  size  of  engine  or  turbine, 
and  also  upon  the  type  of  machine.  The  theoretical  gain  for  a 
perfect  steam  motor  per  inch  of  vacuum  will  vary  from  about 
3.0  per  cent,  at  25  inches  vacuum  to  about  5.0  per  cent,  at  28 
inches  vacuum.  A  well  designed  steam  turbine  will  very  nearly 
realize  the  theoretical  gains  for  any  given  vacuum.  A  high 
vacuum  means  low  temperature  condensed  steam,  and  this  may 
necessitate  the  heating  of  condensed  steam  before  it  is  used  as 
boiler  feed  water. 

If  an  engine  or  turbine  is  provided  with  some  vessel  into  which 
the  steam  is  exhausted,  vacuum  could  be  maintained  by  simply 
removing  the  uncondensed  exhaust  steam  as  fast  as  it  enters. 
Such  a  method,  however,  would  not  be  economical,  as  the  equip- 
ment utilized  in  maintaining  the  vacuum  would  have  to  handle 
practically  the  entire  volume  of  exhaust  steam  leaving  the  engine. 
If  this  were  the  case,  very  little  gain  would  result,  for  as  much 
work  would  have  to  be  done  by  the  condenser  pump  in  main- 
taining the  lower  back  pressure  as  would  be  gained  by  the  engine. 

164 


ENGINE  AND  TURBINE  AUXILIARIES         165 

Steam,  however,  may  easily  be  condensed,  and  in  the  form  of 
water  occupies  a  very  much  smaller  volume.  Advantage  of  this 
fact  is  taken  in  the  operation  of  condensers.  Thus,  if  the  exhaust 
steam  from  the  engine  is  admitted  into  a  vessel  and  condensed 
before  being  discharged,  the  work  required  to  maintain  the  vacuum 
is  greatly  reduced,  because  the  work  of  the  condenser  pump  is 
only  that  due  to  the  removal  of  a  comparatively  small  volume 
of  water. 

In  a  system  composed  entirely  of  steam,  or  one  in  which  the 
exhaust  steam  was  not  mixed  with  air  or  with  other  gases  which 
have  entered  the  system,  the  vacuum  to  be  maintained  is  depend- 
ent upon  the  temperature  of  the  condensed  steam.  By  refer- 
ence to  the  steam  tables  (Table  5),  it  will  be  found  that  water  at 
a  temperature  of  126.1  degrees  Fahrenheit  boils  at  a  pressure  of 
2  pounds  absolute.  A  condenser  in  which  the  condensed  steam 
is  at  that  temperature  would  be  limited  to  that  pressure.  Any 
attempt  to  lower  the  vacuum  would  cause  an  evaporation  of  the 
condensed  steam. 

In  the  actual  operation  of  condensers  the  temperature  of  the 
condensed  steam  must  be  below  that  corresponding  to  the 
vacuum  to  be  carried.  The  condenser  is  never  free  from  air  and 
the  temperature  of  the  condensed  steam  is  several  degrees  below 
that  corresponding  to  the  vacuum  carried.  Air  enters  with  the 
boiler  feed  water  and  also  leaks  in  the  condenser  through  piping 
and  valves.  The  air  mixed  with  the  steam  not  only  tends  to 
destroy  the  vacuum  and  raise  the  pressure  in  the  condenser  above 
that  theoretically  required,  but  must  also  be  continuously 
removed,  if  the  vacuum  is  to  be  maintained. 

The  Measurement  of  Vacuum. — The  pressure  maintained  in 
a  condensing  system  may  be  measured  by  a  mercury  manometer 
or  by  a  special  gage.  The  pressure  is  below  that  of  the  atmos- 
phere, hence  the  term  vacuum  is-  applied. 

The  measurement  of  pressures  above  that  of  the  atmosphere  is 
expressed  in  pounds  gage.  In  the  measurement  of  pressures 
below  atmosphere,  the  unit  of  pressure  is  usually  stated  in  inches 
of  mercury  and  expresses  the  amount  of  pressure  below  that  of 
the  atmosphere.  To  convert  pressure  above  atmospheric  to 
absolute  pressure,  the  gage  pressure  is  added  to  the  atmospheric 
pressure,    corresponding    to    the    barometric    reading.     When 


166        STEAM  AND  GAS  POWER  ENGINEERING 

vacuum  readings  have  to  be  converted  into  absolute  pressures, 
the  pressure  corresponding  to  the  vacuum  must  be  deducted 
from  the  atmospheric  pressure. 

As  an  illustration,  a  condensing  engine  receives  steam  at 
100  pounds  per  square  inch  gage  and  exhausts  into  a  condenser 
whose  gage  reads  26  inches  of  mercury.  The  barometric  pres- 
sure is  29  inches  of  mercury. 

A  column  of  mercury  1  inch  high  is  equivalent  to  a  pressure 
of  0.491  (roughly  %)  pounds  per  square  inch,  or  the  equivalent 
pressure  of  the  atmosphere  is  then : 

29  X  0.491  =  14.24  pounds  per  square  inch. 
The  absolute  pressure  of  the  entering  steam  is: 

100  +  14.24  =  114.24  pounds  per  square  inch. 

Since  the  vacuum  in  the  condenser  is  measured  in  units  below 
atmospheric  pressure  the  absolute  pressure  within  the  condenser 
is: 

29  —  26  =  3  inches  of  mercury 
which  is  equivalent  to  ■ 

3  X  0.491  =  1.47  pounds  per  square  inch  absolute. 

Types  of  Condensers. — Condensers  are  either  of  the  jet  or  of 
the  surface  type.  The  jet  condensers  produce  condensation 
by  the  direct  mingling  of  the  exhaust  steam  and  circulating  water, 
and  the  resulting  mixture  of  condensed  steam  and  water  leaves 
the  condenser  at  the  same  temperature.  In  the  surface  con- 
denser, the  exhaust  steam  and  the  circulating  water  are  separated 
by  tubes,  the  heat  transfer  between  the  steam  and  circulating 
water  taking  place  by  conduction  through  the  tubes. 

The  jet  condenser  is  much  simpler  than  the  surface  condenser 
and  its  first  cost  is  lower,  but  in  most  cases  it  is  restricted  in  its 
application  to  plants  where  the  injection  water  is  good.  The 
surface  condenser  has  the  advantage  in  that  its  cooling  water 
does  not  come  in  direct  contact  with  the  steam  to  be  condensed. 
For  this  reason  surface  condensers  are  used  where  the  condensed 
steam  is  returned  to  the  boiler,  and  where  the  cooling  water  is 
salty,  muddy,  or  otherwise  unfit  for  steam  making.  While  the 
surface  condenser  is  particularly  well  suited  for  plants  where  the 
circulating  water  is  poor,  it  must  not  be  inferred  that  it  would  be 
practical  to  use  water  so  filthy  that  it  would  foul  the  tubes. 


ENGINE  AND  TURBINE  AUXILIARIES 


167 


Jet  Condensers. — Fig.  136  illustrates  the  construction  of  one 
of  the  simpler  types  of  jet  condensers.  Exhaust  steam  enters 
at  A.  Injection  water  enters  at  B,  and  is  divided  into  a  fine 
spray  by  the  adjustable  valve  D.  The  steam  is  condensed  by 
contact  with  the  finely  sprayed  water,  and 
the  mixture  accumulates  in  chamber  F, 
from  which  it  passes  to  the  pump  G  and 
is  discharged  at  J.  The  pump  G  in  this 
type  of  condenser  must  remove  both  the 
air  and  the  condensed  steam.  It  is  called  a 
wet  air  pump.  The  pump  cylinder  in  order 
to  handle  the  air  and  the  condensed  steam 
must  be  designed  larger  than  would  be 
required  for  the  removal  of  the  water 
alone. 

Injection  water  under  pressure  is  not 
necessary  with  this  type  of  condenser,  as 
the  water  will  be  drawn  into  the  con- 
densing chamber  by  the  vacuum  produced, 
although  the  pumping  head  in  such  cases 
is  limited  to  about  15  feet.     With  such  an 


Fig.  136. — Jet  condenser. 

arrangement,  means  must  be  provided  for  creating  a  vacuum  when 
starting  the  condenser.  This  is  usually  accomplished  by  start- 
ing the  pump  or  by  providing  the  condenser  with  an  auxiliary 
supply  of  injection  water  under  pressure,  which  will  produce 
sufficient  vacuum  by  condensing  the  first  steam  admitted. 


168        STEAM  AND  GAS  POWER  ENGINEERING 

Condensers  are  usually  provided  with  some  means  for  auto- 
matically breaking  the  vacuum.  The  atmospheric  relief  valve, 
illustrated  in  Fig.  137,  is  placed  in  a  branch  taken  from  the  main 
exhaust  line  between  the  condenser  and  the  engine,  and  leading 
to  the  atmosphere.  The  atmospheric  exhaust  valve  is  held 
closed  by  the  atmospheric  pressure  when  the  vacuum  is  main- 
tained, but  should  the  vacuum  be  lost  the  pressure  of  the  exhaust 
steam  operates  the  valve,  permitting  a  free  outlet  of  the  steam  to 
the  atmosphere.  When  the  vacuum  is  restored,  the  valve  will 
automatically  close. 


Fig.  137. — Atmospheric  relief  valve. 

Barometric  Condensers. — Fig.  138  illustrates  the  barometric 
type  of  jet  condenser.  The  condensing  chamber  is  supported 
upon  a  water -sealed  tail  pipe,  34  feet  above  the  surface  of  the 
water  in  the  hot  well.  Atmospheric  pressure  at  sea  level  will 
support  a  column  of  water  34  feet  high,  consequently  the  accu- 
mulation of  condensed  steam  in  the  tail  pipe  which  would  tend  to 
rise  above  this  height,  will  displace  an  equal  quantity  of  water 
from  the  bottom  of  the  tail  pipe.  No  pump  is  required  for  the 
removal  of  the  condensed  steam  from  the  barometric  condenser, 
but  in  most  cases  the  use  of  a  pump  for  the  injection  water  is 


ENGINE  AND  TURBINE  AUXILIARIES 


169 


necessary.     If  the  cold  water  supply  is  within  a  vertical  distance 
of  20  feet  from  the  injection  opening  to  the  condenser,  the  use  of 


water  distributing 

TRAY 


AlR  PUMP  SUCTION 


Fig.   138. — Sectional  views  of  a  barometric  condenser. 

a  pump  for  the  injection  water  may  be  dispensed  with,  as  the 
vacuum  will  lift  the  water  to  that  extent. 


170        STEAM  AND  GAS  POWER  ENGINEERING 

Ejector  Condensers. — The  ejector,  eductor,  and  siphon 
types  of  jet  condensers  depend  upon  the  high  momentum  of  the 
condensed  steam  and  cooling  water  to  discharge  the  condensate 


Fig.  139. — Ejector  condensers. 


against  atmospheric  pressure.  No  circulating  or  air  pump,  or 
barometric  tube  is  needed.  Fig.  139  illustrates  two  different 
types  of  such  condensers.     Exhaust  steam  enters  the  eductor 


ENGINE  AND  TURBINE  AUXILIARIES  171 

condenser  at  E,  completely  fills  the  annular  chamber  A,  and 
passes  through  the  small  nozzles.  The  cooling  water  is  con- 
tinuously drawn  in  through  the  nozzle  C  and  meets  the  condensed 
steam  in  the  tube  T.  Condensation  takes  place  and  sufficient 
velocity  is  developed  to  remove  the  condensed  steam,  the  cooling 
water,  and  the  air. 

Surface  Condensers. — A  sectional  elevation  through  a  surface 
condenser  is  shown  in  Fig.  140.  It  consists  of  a  cylindrical  or 
rectangular  cast  iron  shell  closed  at  the  two  ends  by  suitable 
heads.  Attached  to  the  inner  surface  of  the  condenser  shell 
are  two  tube  plates,  which  are  joined  by  numerous  seamless  drawn- 
brass  tubes. 

Exhaust  steam  enters  the  top  of  the  condenser  and  strikes 
a  baffle  plate  which  protects  the  upper  rows  of  tubes  and  dis- 
tributes the  steam  to  all  parts  of  the  condenser.  Circulating 
water  enters  at  the  end  of  the  condenser,  and  passes  through  the 
various  banks  of  tubes  as  shown  by  the  arrows.  The  steam  flows 
around  the  tubes  and  is  condensed  by  coming  in  contact  with 
the  cool  surfaces. 

In  the  condenser  illustrated,  the  circulating  and  wet  air  pump 
form  the  base  upon  which  the  condenser  rests,  although  this 
arrangement  is  not  always  adhered  to.  The  pumps  (Fig.  140) 
are  connected  by  a  common  piston  rod  which  is  operated  by  the 
central  steam  cylinder. 

Vacuum  Pumps 

In  connection  with  a  condenser  installation,  a  wet-air  pump 
and  a  circulating  pump  are  required.  To  maintain  a  high  vacuum, 
a  dry-air  pump  is  used  in  addition  to  a  hot-well  pump  and  a  water 
circulating  pump.  The  power  consumed  by  the  condenser  aux- 
iliaries is  about  2  per  cent,  of  the  total  output  of  the  unit  the 
condenser  serves.  Wet-air  pumps  are  used  to  remove  the  con- 
densed steam,  the  non-condensible  vapors,  and  the  cooling  water. 
Dry-air  pumps  remove  only  the  non-condensible  vapors,  and 
are  used  in  steam  turbine  installations  where  a  high  vacuum  must 
be  maintained.  Hot-well  or  condensate  pumps  are  those  that 
remove  the  condensate  from  surface  condensers;  circulating 
pumps  force  the  cooling  water  through  the  condenser. 


172        STEAM  AND  GAS  POWER  ENGINEERING 


ENGINE  AND  TURBINE  AUXILIARIES 


173 


Wet-air  Pumps. — A  type  of  wet-air  pump  commonly  used  in 

connection  with  jet  condensers  is  illustrated  in  Fig.  141.     These 

pumps  are  of  the  reciprocating  type.     On  the  upward  stroke  of 

the  piston,  a  lower  pressure 

than  that  maintained  in  the 

condenser    is    created   below 

the  piston,  causing  the  cool- 
ing   water    and    condensate, 

together  with  the  air,  to  be 

drawn  into  the  cylinder.    The 

downward  stroke  of  the  piston 

causes  the  foot  val  ves  to  close 

and  the  entrapped  water  and 

air  to  pass  through  valves  in 

the  piston.     When  the  piston 

next  moves  upward  the  mix- 
ture   is   compressed    by    the 

closure  of  the  valves  in  the 

piston     and     is     discharged 

through  the  valves  at  the  top 

of  the  cylinder. 

Edwards  Air  Pump. — Fig.  142  illustrates  a  type  of  wet-air 

pump  designed  for  use  with  surface  condensers.     Pumps  that 

depend  upon  foot  valves  for  the  entrapping  of  the  air  and  water  in 

the  pump  cylinder  require  an  appre- 
ciable difference  in  pressure  to  insure 
the  opening  of  the  val  ves.  The  Edwards 
air  pump,  by  the  elimination  of  these 
valves,  is  capable  of  maintaining  a  vac- 
uum from  Y^  to  1  inch  lower  than  would 
be  possible  with  pumps  of  the  valve 
operated  type. 

The  condensed  steam  flows  by  grav- 
ity from  the  condenser  to  the  pump, 
where   it  collects   in  the  base.     Upon 

Fig.  142.-Edwards  air  pump.   the  degcent  Qf  the  CQnical  shaped  pistons 

or  bucket,  the  water  is  projected  at  high  velocity  through  the 
ports  into  the  working  barrel  of  the  pump,  drawing  with  it  con- 
siderable air  and  other  non-condensible  vapors.     On  the  upward 


Fig.   141. — Wet-air  pump. 


174       STEAM  AND  GAS  POWER  ENGINEERING 

stroke,  the  ports  are  closed  by  the  piston,  and  the  water  and 
entrapped  air  is  discharged  through  the  valve  at  the  top  of  the 
cylinder. 

Dry-air  Pumps. — For  high  vacua,  it  is  more  desirable  to  dis- 
charge the  air  and  condensate  from  the  condenser  separately. 
This  arrangement  necessitates  the  use  of  two  pumps,  a  dry-air 
pump  and  a  wet-air  pump. 

Fig.  143  illustrates  a  sectional  view  of  an  Alberger  dry-air 
pump.     The  suction  valve  is  positively  actuated  by  an  eccentric 


Fig.  143. — Dry-air  pump. 


on  the  crank  shaft.  This  valve  is  provided  with  an  equalizing 
port,  which  eliminates  the  detrimental  influence  of  the  air  in  the 
clearance  space. 

When  the  piston  reaches  the  end  of  the  stroke,  the  space  be- 
tween it  and  the  cylinder  head  is  filled  with  air  at  atmospheric 
pressure  that  has  not  been  discharged  through  the  outlet  valve. 
If  the  piston  were  to  make  the  return  stroke  while  this  air  was 
under  pressure,  a  considerable  part  of  the  stroke  would  be  tra- 
versed by  the  piston  before  this  air  had  expanded  to  the  suction 
pressure.     As  a  result  the  drawing  in  of  a  fresh  charge  of  air 


ENGINE  AND  TURBINE  AUXILIARIES 


175 


from  the  condenser  would  be  confined  to  a  small  portion  of  the 
stroke.  To  increase  the  effectiveness  of  the  pump,  the  valve  is 
moved  into  its  equalizing  position  before  the  piston  begins  its 
return  stroke.  The  air  under  pressure  is  then  transferred  to  the 
other  side  of  the  piston,  where  it  is  compressed  and  is  discharged 
through  the  valves  at  the  top  of  the  cylinder.  By  this  means  the 
suction  side  of  the  piston  is  effective  throughout  its  entire  stroke. 
Circulating  Pumps. — While  reciprocating  pumps  are  used  to  a 
very  large  extent  in  condenser  operation  as  dry-  and  as  wet-air 


Single  stage  centrifugal  pump. 


pumps,  centrifugal  pumps  are  generally  used  as  circulating 
pumps  supplying  cooling  water  to  surface  condensers.  Centrifu- 
gal pumps  are  also  used  as  hot-well  pumps. 

Fig.  144  illustrates  a  section  through  a  single  stage  centrifugal 
pump.  It  consists  of  a  rotary  impeller,  into  which  the  water  is 
drawn  and,  because  of  the  centrifugal  force,  leaves  the  tips  of  the 
rotor  at  high  velocity.  The  casing  of  the  pump  guides  the  water 
from  the  propeller  to  the  discharge  outlet.  No  valves  are 
required  in  this  type  of  pump. 

The  single  stage  pump  is  limited  in  its  application  to  compara- 


17G        STEAM  AND  GAS  POWER  ENGINEERING 

tively  low  heads  or  pressures.  For  high  heads  a  greater  number 
of  stages  are  used.  In  these  the  water  is  discharged  from  one 
rotor  to  the  next,  each  rotor  acting  as  a  booster.  However, 
condenser  operation  requires  comparatively  low  heads  and  the 
single  stage  pump  will  be  found  sufficient  for  most  installations. 

Cooling  Ponds  and  Cooling  Towers 

Reclaiming  Cooling  Water. — The  quantity  of  cooling  water 
required  to  condense  steam  varies  from  30  to  70  pounds  for  each 
pound  of  steam  condensed.  In  many  plants  this  water,  after 
passing  through  the  condenser,  is  wasted;  hence  a  continuous 
supply  of  fresh  water  is  required.  In  localities  where  water  is 
plentiful  and  its  cost  is  low,  this  practice  may  be  correct,  but 
many  plants  are  handicapped  on  account  of  the  scarcity  or 
high  cost  of  water.  In  such  cases  the  saving  of  cooling  water  is 
an  important  problem.  Several  methods  have  been  developed 
to  cool  the  condenser  circulating  water  so  that  it  can  be  used 
repeatedly. 

The  means  for  reclaiming  the  water  usually  adopted  at  the 
present  time  depends  upon  the  cooling  effect  derived  from  the 
evaporation  of  water.  Air  has  the  property  of  evaporating  and 
absorbing  water.  The  amount  of  water  absorbed  depends  upon 
the  condition  of  the  air,  while  the  rate  of  evaporation  depends 
upon  the  velocity  and  degree  of  contact  between  the  air  and 
water.  As  an  illustration,  air  at  a  temperature  of  90°F.  and  50 
per  cent,  humidity,  which  signifies  that  the  air  is  only  one-half 
saturated,  would  be  theoretically  capable  of  cooling  condenser 
circulating  water  to  75°F.,  or  15°  below  the  temperature  of  the 
atmosphere.  On  the  other  hand,  on  a  wet  rainy  day,  when  the 
air  is  saturated  with  moisture,  little  or  no  cooling  effect  could 
be  produced  by  evaporation,  for  the  air  contains  nearly  as  much 
water  as  it  will  absorb. 

The  following  three  systems  are  used  for  reclaiming  condenser 
circulating  water:  cooling  ponds,  spray  ponds,  and  cooling 
towers. 

When  reclaiming  circulating  water  by  any  of  the  above 
methods,  an  allowance  of  2  to  8  per  cent,  should  be  made  for 
evaporation. 


ENGINE  AND  TURBINE  AUXILIARIES  177 

Cooling  Ponds. — Cooling  ponds  or  tanks  depend  for  their 
cooling  effect  upon  the  exposure  of  a  comparatively  large  area 
of  water  to  the  air.  In  these  the  water  is  cooled  partly  by  radia- 
tion but  principally  by  evaporation.  The  cooling  is  dependent 
upon  the  surface  exposed  and  consequently  cooling  ponds  are 
usually  shallow,  but  spread  over  a  considerable  area.  The  hot 
water  from  the  condenser  enters  the  pond  at  one  point,  and  is 
cooled  by  surface  evaporation  when  it  reaches  the  intake  point 
to  the  condenser. 

Cooling  ponds  are  very  simple,  but  are  open  to  the  objection 
that  the  evaporation  is  slow.  Furthermore  they  may  freeze 
in  winter,  and  thus  cut  off  the  supply  of  condensing  water. 

Spray  Ponds. — In  this  system  the  hot  water  from  the  condenser 
is  cooled  by  spraying  it  into  the  air  so  that  it  falls  in  a  thin  mist 
into  the  basin  or  pond  below.  The  spray  brings  the  air  and  water' 
into  intimate  contact,  exposes  a  large  amount  of  water  surface 
to  the  air,  and  consequently  produces  a  large  cooling  effect  in  a 
comparatively  small  space.  The  water  is  pumped  from  the 
condenser  and  is  forced  through  the  spray  nozzles  under  pres- 
sure. Sufficient  cooling  is  effected  by  the  fine  spray  so  that  the 
water  may  be  immediately  returned  to  the  condenser. 

When  compared  with  the  cooling  pond,  the  spray  pond  occupies . 
less  space.  A  pond  depending  upon  natural  evaporation  would 
be  approximately  50  times  as  large  as  a  spray  pond  for  the  same 
cooling  capacity.  In  cases  where  the  cooling  effect  is  not  suffi- 
cient in  a  single  spraying,  the  water  may  be  forced  through  the 
nozzles  a  second  time,  thus  securing  a  double-cooling  effect. 

Cooling  Towers. — A  cooling  tower  consists  of  a  wooden,  sheet 
iron,  or  concrete  chamber  that  is  filled  with  mats  made  of  steel 
wire,  wooden  slats,  or  tile.  Hot  water  from  the  condenser  is 
elevated  to  the  top  of  the  tower  and  is  distributed  evenly  over 
the  top  surface.  The  water  in  descending  is  retarded,  is  broken 
up  by  the  mats,  and  is  thus  brought  in  intimate  contact  with  the 
air  that  ascends  through  the  tower. 

The  method  of  supplying  the  air  to  cooling  towers  gives  rise 
to  three  classifications:  open  towers  or  atmospheric  coolers; 
natural-draft  towers;  forced-draft  towers. 

The  open  tower  is  the  simplest,  although  it  requires  larger 
ground  space.     The  mats  are  supported  on  a  tower  of  open  grill 
12 


178        STEAM  AND  GAS  POWER  ENGINEERING 

work,  so  arranged  that  the  descending  water  will  be  subjected 
to  the  slightest  wind.  This  type  of  tower  has  proved  successful 
in  localities  where  the  climate  is  dry  and  where  winds  prevail. 


Fig.  145. — Forced-draft  cooling  tower. 


The  natural-draft  or  flue  tower  depends  for  its  cooling  upon  the 
flow  of  air,  which  results  when  the  air  within  the  tower  and  that 
without  are  at  different  densities.     The  air  within  the  tower 


ENGINE  AND  TURBINE  AUXILIARIES 


179 


will  always  be  the  lighter  because  of  its  higher  temperature  and 
because  of  the  greater  amount  of  moisture  it  contains.  The 
necessary  velocity  of  air  through  the  tower  can  be  made  as  de- 
sired by  proportioning  the  height  of  the  tower.  The  natural- 
draft  tower  is  entirely  enclosed,  except  at  top  and  bottom.  The 
condenser  water  is  distributed  at  the  top,  while  the  air  becoming 
heated  is  displaced  by  the  colder  air  which  enters  at  the  base  of 
the  tower.  These  towers  are  suitable  for  locations  where  space 
requirements  would  prohibit  the  open  or  atmospheric  tower. 

The  forced-draft  tower  lends  itself  to  practically  all  locations 
and  conditions.  Fig.  145  illustrates  a  sectional  view  of  a  forced- 
draft  tower.  This  type  of  tower  is  operated  in  the  same  manner 
as  other  cooling  towers,  but  a  fan  is  used  to  create  the  flow  of  air 
through  the  descending  water. 

These  towers  are  light  and  compact,  requiring  about  one-fifth 
the  space  occupied  by  a  tower  of  the  natural-draft  type.  They- 
are  entirely  independent  of  the  natural  circulation  of  the  air, 
and  are  consequently  more  reliable.     The  A 

power  required  to  operate  a  forced-draft 
cooling  tower  will  vary  from  2%  to  4  per 
cent,  of  the  total  power  generated  by  the 
main  units. 

Sepabators 


Steam  Separators. — The  function  of 
a  steam  separator  is  to  protect  engines 
and  turbines  from  the  dangerous  results 
that  might  occur  if  large  quantities  of 
water  or  grit  enter  them.  When  the 
boiler  is  improperly  proportioned  or 
when  it  is  forced  above  its  rating,  there 
is  a  possibility  of  large  amounts  of  water 
being  carried  over  with  the  steam.  The 
condensation  that  occurs  in  long  pipe 
lines   adds   to  the  water  in  the  steam. 


Fig 


1  46.  —  Steam 
separator. 


The  steam  separator 
automatically  separates  the  water  from  the  steam,  thus  pro- 
tecting the  cylinder,  and  at  the  same  time  promotes  lubrica- 
tion by  preventing  the  washing  action  that  results  when  wet 
steam  is  used  in  the  engine  cylinder. 


180        STEAM  AND  GAS  POWER  ENGINEERING 


Fig.  146  illustrates  one  type  of  steam  separator.  The  flow 
of  the  steam  in  passing  through  the  separator  is  interrupted  by 
corrugated  plates.  The  momentum  of  the  heavier  particles  of 
water  causes  them  to  be  thrown  out,  and  they  adhere  to  the  sur- 
face of  the  baffle.  The  separated  water  then  flows  by  gravity 
to  the  trap  or  receiver  below,  from  which  it  is  drained. 

Separators  are  made  in  various  sizes,  depending  upon  the  size 
of  the  pipe  to  which  they  are  to  be  attached.  They  may  be 
used  on  vertical,  horizontal,  or  angle  pipes.  Special  separators, 
known  as  the  receiver  type,  with  an  extra  large  water  storing 
capacity  are  made  and  are  usually  installed  in  plants  having  long 
pipe  systems,  where  there  is  a  possibility  of  large  quantities  of 
water  suddenly  passing  through  with  the  steam. 

The  separator  should  be  placed 
as  close  to  the  steam  chest  of  the 
engine  as  possible.  The  receiver 
type  of  separator  is  preferable  if 
the  engine  load  is  intermittent  or 
fluctuates  rapidly. 

Exhaust-steam  and  Oil  Separa- 
tors. —  Exhaust-steam  separators 
are  constructed  on  the  same  prin- 
ciples as  steam  separators,  but 
their  function  is  to  remove  oil  that 
may  be  contained  in  the  exhaust 
steam.  The  use  of  a  good  oil 
separator  between  the  engine  and 
the  condenser  will  eliminate  the  oil 
from  the  condensate,  thus  making 
it  satisfactory  as  boiler  feed  water. 
In  the  case  of  surface  condensers, 
oil  separators  prevent  the  fouling 
of  the  condenser  tubes  by  the  oil 
which  would  lower  the  efficiency  of  the  condenser  if  allowed  to 
accumulate. 

In  exhaust  steam  heating  the  oil  separator  is  used  to  remove  the 
oil  from  the  steam  before  it  enters  the  heating  system.  Oil 
in  the  steam  would  coat  the  inner  surface  of  radiators  with  a 


Fig.   147. — Exhaust  head. 


ENGINE  AND  TURBINE  AUXILIARIES  181 

thin  layer  of  grease  which  would  soon  impair  the  amount  of  heat 
transmitted  through  them. 

In  the  use  of  feed-water  heaters,  the  oil  separator  may  be 
entirely  independent  and  separately  installed,  but  in  most 
cases,  it  is  made  a  part  of  the  heater  itself. 

In  plants  where  low  pressure  turbines  are  utilized,  an  oil 
separator  is  placed  between  the  engine  and  the  turbine.  The 
moisture  and  oil  are  thus  removed  from  the  exhaust  steam 
before  it  enters  the  turbine. 

Exhaust  Heads. — Fig.  147  illustrates  a  section  through  an 
exhaust  head.  This  device  is  used  to  prevent  the  deposit  of  any 
moisture  or  oil  upon  roofs  and  side  walks  when  the  exhaust  from 
an  engine  is  allowed  to  escape  to  the  atmosphere.  Exhaust 
heads  are  attached  in  a  vertical  position  at  the  end  of  the  atmos- 
pheric exhaust  pipe.  Their  principle  of  operation,  like  that  of 
the  separator,  depends  upon  the  changing  of  the  course  of  the 
steam.  The  moisture  and  oil  thrown  out  by  centrifugal  force 
collect  at  the  bottom  of  the  head  and  are  drained  to  waste. 

Problems 

1.  Compare  the  volumes  of  steam  and  of  water  at  atmospheric  pressure. 

2.  Compare  the  volume  of  one  pound  of  steam  at  atmospheric  pressure 
with  the  volumes  at  26  inches  vacuum,  28  inches  vacuum,  and  29  inches 
vacuum. 

3.  A  condenser  gage  registers  28.5  inches  of  mercury.  The  barometer 
registers  29.35  inches  of  mercury.  What  is  the  absolute  pressure  of  the  air 
in  pounds  per  square  inch?  What  is  the  absolute  pressure  in  the  condenser 
in  pounds  per  square  inch? 

4.  Make  a  sketch  of  the  exhaust  piping  between  an  engine  and  a  condenser 
showing  the  location  of  the  atmospheric  relief  valve. 


.  CHAPTER  X 
STEAM  POWER  PLANT  TESTING 

General  Rules. — The  chief  object  in  the  testing  of  power  plant 
equipment  is  to  secure  data  from  which  the  ccst  of  operation  may 
be  calculated.  Tests  are  also  carried  on  for  the  purpose  of  com- 
paring actual  with  guaranteed  results  as  to  capacity  and  efficiency 
of  the  complete  power  plant  or  of  the  separate  parts.  The 
effect  of  different  conditions  of  operation  or  of  changes  in  design 
can  also  be  determined  by  test. 

The  test  of  a  power  plant  is  essentially  a  test  of  each  of  the 
various  main  parts;  it  is  a  combined  test  of  the  steam  boiler, 
of  the  steam  engine  or  turbine,  and  of  the  other  power  plant 
equipment. 

The  testing  of  a  power  plant  includes  the  measurement  of 
certain  conditions  which  are  important  economically  in  the  opera- 
tion of  the  plant.  This  may  be  done  by  the  reading  of  various 
appliances  at  specified  intervals  when  the  test  is  in  progress  or 
by  the  use  of  special  instruments  of  the  recording  type.  The 
recording  instrument  gives  a  continuous  record  which  is  often 
desirable  in  studying  the  daily  operation  of  the  plant.  In  reality, 
with  recording  instruments,  the  plant  is  continuously  under  test 
and  any  variation  that  may  occur  from  day  to  day  is  indicated 
graphically.  The  economy  test  consists,  in  general,  in  the 
measurement  of  the  amount  of  heat  supplied  and  the  amount  of 
energy  that  has  been  transformed  into  useful  work. 

In  testing  a  boiler,  the  amount  of  coal  fired  would  give  a  direct 
measure  of  the  heat  supplied.  To  find  the  amount  of  energy 
transformed,  the  weight  of  the  water  evaporated,  the  quality 
of  the  steam  generated,  the  pressure  in  the  boiler,  and  the  tem- 
perature of  the  entering  feed  water  must  be  measured.  To  assist 
in  determining  the  extent  of  the  losses  in  a  boiler  plant,  such 
readings  as  the  temperature  of  the  flue  gases,  the  draft  at  various 
points  in  the  boiler,  and  the  analysis  of  the  flue  gases  are  usually 
taken. 

182 


STEAM  POWER  PLANT  TESTING  183 

The  testing  of  the  engine  or  turbine  consists  in  measuring  the 
weight  of  the  steam  supplied  together  with  its  quality  and  pres- 
sure at  the  throttle  as  well  as  the  pressure  of  the  exhaust;  from 
this  data  the  heat  supplied  to  the  motor  may  be  calculated.  The 
delivered  power  is  measured  by  a  Prony  brake,  an  electrical 
generator,  or  some  other  form  of  dynamometer.  As  in  the  case 
of  the  boiler,  .many  other  readings  are  taken  during  the  test. 
These  consist  of  such  data  as  indicator  cards,  in  the  case  of  re- 
ciprocating steam  engines;  the  amount  of  condensing  water,  and 
various  temperatures  at  the  condenser. 

Preparing  for  the  Test. — A  thorough  examination  should  be 
made  of  the  physical  condition  of  all  parts  of  the  plant  including 
boilers,  furnaces,  settings,  engine  cylinders,  piping,  valves, 
etc.  Prior  to  the  test  any  defects  that  may  make  the  results  of 
the  test  unfavorable  should  first  be  remedied.  In  boilers,  for 
example,  any  abnormal  leakage  found  at  the  tubes,  rivets,  or 
metal  joints  should  be  repaired.  All  leakage  from  blow-offs, 
drips,  etc.,  or  through  any  steam  or  water  connections  which 
might  affect  the  results  should  be  prevented.  In  preparing  for 
the  test  the  dimensions  of  the  principal  parts  of  apparatus  to  be 
tested  should  be  taken  and  recorded.  Before  the  test  is  started 
it  is  important  that  the  apparatus  to  be  tested  has  been  in 
operation  a  sufficient  length  of  time  to  attain  proper  operating 
conditions. 

Starting  and  Stopping  the  Test. — In  a  plant  operating  con- 
tinuously day  and  night  the  time  for  starting  and  stopping  the 
test  of  a  boiler  should  follow  the  regular  period  of  cleaning 
the  fires.  The  fires  should  be  quickly  cleaned  and  then  burned 
low.  When  this  condition  has  been  reached  the  time  should  be 
noted  as  the  starting  time,  and  the  thickness  of  the  coal  bed, 
the  water  level  in  the  boiler,  and  the  steam  pressure  should  be 
noted.  At  the  close  of  the  test  following  a  regular  cleaning,  the 
fires  should  again  be  burned  low,  and  when  this  condition  has 
become  the  same  as  that  observed  at  the  beginning,  the  water 
level  and  steam  pressure  also  being  the  same,  the  time  is  noted 
and  the  test  is  stopped. 

Weighing  the  Fuel. — The  approved  method  of  weighing  the 
fuel  burned  in  a  specified  interval  of  time  is  by  the  use  of  ordinary 
platform  scales.    If  accurate  results  are  to  be  secured  it  is  not 


184        STEAM  AND  GAS  POWER  ENGINEERING 


recommended  to  weigh  the  fuel  in  a  wheelbarrow  or  similar 
conveyance  full  of  coal  and  assume  that  all  other  loads  brought 
into  the  plant  weigh  the  same;  it  is  also  inaccurate  to  base  the 
weight  of  the  fuel  upon  the  number  of  strokes  of  the  plunger 
in  certain  types  of  stokers.  Even  in  the  use  of  scales  care  must 
be  taken  to  test  their  reliability  by  calibrating  them  with  stan- 
dard weights.  In  case  the  use  of  scales  is  impracticable,  sacks 
or  bags  containing  a  known  weight  of  coal,  as  measured  by  a 
platform  scale,  may  be  used  to  good  advantage. 

Large  plants  in  which  coal  handling  machinery  has  been 
installed  use  weighing  hoppers  to  measure  the  coal  fed  to  the 
boilers.  As  usually  installed  the  weighing  hopper  is  placed  be- 
tween the  main  storage  bunker  in  the  loft  of  the  plant  and  the 
stoker  hoppers  below.  Coal  from  the  main  bunker  passes  first 
to  the  weighing  hopper.  After  being  weighed  the  coal  is  dis- 
tributed to  the  stoker  hoppers.  The  weighing  hopper  travels 
upon  a  special  overhead  track  which  makes  it  possible  for  one 
weighing  hopper  to  serve  several  boilers.  The  scale  beams  and 
levers  extend  downward  so  that  the  poise  on  the  weighing  beam 
is  read  from  the  boiler  room  floor. 

Weighing  the  Feed  Water. — The  most  satisfactory  method 
for  weighing  the  feed  water,  which  is  the  weight  of  the  water 
evaporated  by  the  boiler,  consists  in  the  use  of  one  or  more  tanks 

each  placed  upon  platform  scales. 
These  are  elevated  a  sufficient  dis- 
tance above  the  floor  to  empty  into 
a  receiving  tank,  which  is  in  turn 
connected  to  the  boiler  feed  pump. 
When  only  one  tank  is  available  the 
receiving  tank  should  be  of  sufficient 
size  to  afford  a  reserve  supply  to 
the  pump  while  the  weighing  tank 
is  filling. 

A  great  many  types  of  water  meters  are  sold  commercially  and 
are  often  used  in  measuring  the  feed  water.  To  insure  a  fair 
degree  of  accuracy  the  meter  should  be  calibrated  before  and 
after  the  test  under  the  identical  conditions  it  is  required  to 
operate. 

The  measurement  of  large  quantities  of  hot  water  is  usually 


Fig.  148. — Triangular  weir. 


STEAM  POWER  PLANT  TESTING 


185 


accomplished  by  the  use  of  special  types  of  water  meters,  weirs, 
orifices,  or  automatic  water  weighers. 

Fig.  148  illustrates  a  weir  with  a  triangular  notch,  although 
many  other  forms  of  notches  may  be  used.     The  amount  of 


Pipes  to  Manometer 


Inlet 


Outlet 


Fig.   149. — Venturi  meter. 


water  discharged  is  dependent  upon  the  distance  or  head  above  the 
bottom  of  the  weir. 

The  Venturi  meter  is  an  arrangement  of  piping  in  which  there  is 
a  gradual  narrowing  of  the  section  followed  by  a  gradual  enlarge- 
ment. Fig.  149  illustrates  this  type  of  meter.  Tubes  entering 
the  meter  at  the  sections  shown  and  attached  to 
the  manometer  are  used  in  measuring  the  quan- 
tity of  water  delivered. 

Dratt  Gages. — The  simplest  form  of  draft 
gage  is  the  U-tube  or  manometer,  illustrated  in 
Fig.  150.  For  the  measurement  of  draft  the 
tube  is  filled  with  water  and  is  connected  at 
"A"  by  means  of  tubing  to  the  point  where  the 
pressure  is  to  be  measured.  The  amount  of 
pressure  will  be  indicated  by  the  difference  in 
the  level  of  the  liquid  and  may  be  measured  in 
inches  of  water. 

For  the  measurement  of  slight  pressures  an 
inclined  tube,  as  illustrated  in  Fig.  151,  may  be  FlG-  15°- 

7  °  '         J  or  manometer. 

used.     The  bottle  B  to  which  the  inclined  tube 

CD  is  attached  is  filled  with  water.     The  outer  end  of  the  inclined 

tube  is  attached  to  the  chamber  in  which  the  pressure  is  to  be 


-U-tube 


186        STEAM  AND  GAS  POWER  ENGINEERING 

measured.  The  pressure  is  measured  as  with  the  U-tube  (Fig. 
150),  but  by  the  use  of  the  inclined  tube  the  movement  of  one 
inch  in  a  vertical  scale  is  magnified. 


Fig.  151. — Inclined  tube  manometer. 

Temperature  Measurement.  —  Temperatures  are  usually 
measured  by  means  of  one  of  the  following  types  of  thermometers : 
mercurial  thermometers;  electrical  resistance  thermometers; 
mechanical  pyrometers;  thermoelectric  pyrometers. 

The  ordinary  mercury  in  glass  thermometer  is  commonly  used 
for  temperatures  less  than  500°F.;  above  500°  special  nitrogen 
filled  glass  thermometers  must  be  used. 


Fig.  152. — Diagram  of  the  thermoelectric  method  of  temperature  measurement. 

Electrical  resistance  thermometers  are  based  upon  the  prin- 
ciple that  the  resistance  of  certain  metals  changes  with  change  of 
temperature.  The  thermometer  element  is  constructed  of  some 
metal,  like  platinum,  and  the  variation  of  resistance  measured 
by  a  Wheatstone  bridge. 


STEAM  POWER  PLANT  TESTING  187 

Mechanical  pyrometers  consist  of  two  metal-rods  whose  rate 
of  expansion  differ.  The  rods  are  connected  through  gears  and 
levers  to  a  pointer  which  rotates  over  the  dial  graduated  in 
degrees  of  temperature. 

Thermoelectric  pyrometers  are  based  upon  the  principle  that 
an  electromotive  force  is  produced  when  two  wires  of  different 
metals  are  joined  and  heated.  Fig.  152  illustrates  a  thermoelec- 
tric pyrometer.  T  is  a  porcelain  tube  which  holds  the  two  dis- 
similar metal  wires  and  which  is  placed  at  the  point  where  the 
temperature  is  to  be  read.  M  is  a  meter  for  measuring  the  im- 
pressed voltage;  it  is  provided  with  a  scale  calibrated  in  degrees. 

Measuring  the  Weight  of  Steam. — The  most  satisfactory 
method  of  weighing  the  amount  of  steam  consumed  by  the 
engines  or  turbines  is  by  the  use  of  platform  scales  and  surface 
condensers.     This  method  utilizes  two  scales  and  two  tanks 


Trailing  Set 

Leading  Set 
Fig.  153. — Steam  flow  meter  nozzle. 

which  are  alternately  filled  with  condensed  steam  from  the  con- 
denser, weighed,  and  emptied. 

Various  forms  of  steam  meters  may  be  employed  for  measuring 
the  steam,  provided  such  meters  are  properly  calibrated  under 
the  conditions  to  which  they  will  be  subjected  when  in  use. 

Figs.  153  and  154  illustrate  one  type  of  steam  meter.  This 
instrument  measures  the  steam  flow  by  recording  the  velocity. 
The  nozzle  plug  (Fig.  153)  is  inserted  into  the  steam  pipe,  and 
in  this  plug  are  two  sets  of  holes  which  communicate  through 
separate  pipes  to  the  meter  (Fig.  154).  The  leading  set  of  holes 
is  subjected  to  the  velocity  and  the  pressure  of  the  steam  while 
the  trailing  set  is  subjected  only  to  the  pressure.  Their  differ- 
ence records  the  effect  caused  by  velocity. 

The  recording  meter  is  essentially  a  mercury  U-tube  or  mano- 
meter. A  difference  of  pressure  in  the  nozzle  plug  causes  a 
difference  in  height  of  the  mercury.     Change  in  the  position  of 


188        STEAM  AND  GAS  POWER  ENGINEERING 


^ 


Fig.  155. — The  Alden  water  brake. 


STEAM  POWER  PLANT  TESTING 


189 


the  mercury  column  is  measured  by  a  small  float  suspended  from 
pulleys  which  in  turn  move  the  indicating  needle. 

Measurement  of  Power. — One  of  the  simplest  means  of 
measuring  the  power  delivered  by  a 
small  motor  is  by  the  application  of  a 
Prony  Brake  to  the  rim  of  the  wheel  as 
explained  in  Chapter  VII.  For  motors 
of  large  capacity  or  operating  at  high 
speeds  some  other  type  of  dynamometer 
or  an  electrical  generator  must  be  used. 

Another  type  of  brake  for  absorbing 
and  measuring  power  is  some  form  of 
water  friction  brake.  Fig.  155  illustrates 
one  type  of  water  brake.  It  consists  of 
a  disk  A  which  is  connected  to  the  shaft 
S  transmitting  the  power.  The  disk 
revolves  in  a  copper  chamber  filled  with 
oil  while  cooling  is  effected  by  the 
circulation  of  water  around  the  outer 
surface  of  the  copper  chamber.  The 
friction  of  the  oil  producing  the  braking 
effect  is  transmitted  to  the  arm  P  where 
it  is  measured  as  in  the  Prony  brake.  FlG-  156-~ Speed  counter. 

Measurement  of  Speed. — For  determining  the  speed  of  an 
engine  shaft  in  revolutions  per  minute  a  speed  indicator  Fig. 
156  and  watch,  or  a  tachometer  Fig.  157  is  used.     The  tachom- 


Fig.  157. — Tachometer. 


eter  is  more  convenient,  as  it  indicates  on  the  dial  the  revolu- 
tions per  minute. 

Indicator  and  Calorimeters. — Steam  engine  indicators,  steam 
calorimeters,    coal    calorimeters,   and    other   important   instru- 


190        STEAM  AND  GAS  POWER  ENGINEERING 

ments  used  in  power  plant  testing  were  explained  in  previous 
chapters. 

A.  S.  M.  E.  Code. — Complete  and  more  detailed  instructions 
concerning  the  testing  of  steam  power  plants  and  power  plant 
equipment  will  be  found  in  the  Rules  for  Conducting  Performance 
Tests  of  Power  Plant  Apparatus,  published  by  the  American 
Society  of  Mechanical  Engineers. 

Problems 

1.  Examine  some  water  meter  and  explain,  using  clear  sketches,  how  the 
meter  works. 

2.  Explain  the  principles  upon  which  the  construction  of  recording  in- 
struments are  built. 

3.  From  the  A.  S.  M.  E.  Power  Plant  Code  compile  a  table  showing  the 
principal  data  to  be  taken  of  a  test  on  a  non-condensing  steam  power  plant. 


CHAPTER  XI 
INTERNAL  COMBUSTION  ENGINES 

The  internal  combustion  engine,  commonly  called  a  gas  engine, 
differs  from  the  steam  engine,  which  is  an  external  combustion 
motor,  in  that  the  transformation  of  the  heat  energy  of  the  fuel 
into  work  takes  place  within  the  engine  cylinder. 

History. — The  earliest  internal  combustion  engine  was  the 
gunpowder  engine  invented  by  Huyghens  in  1680.  In  the 
Huyghens  engine  a  charge  of  gunpowder  was  introduced  into  a 
vertical  cylinder  filled  with  air  and  exploded ;  the  products  of  com- 
bustion were  driven  out  of  the  cylinder  through  valves,  and  the 
piston,  which  was  at  the  end  of  the  stroke,  was  forced  down  by 
the  atmospheric  pressure  into  the  vacuum  thus  formed. 

The  first  attempt  to  produce  power  from  an  inflammable 
gas,  manufactured  by  the  distillation  of  coal  or  oil,  was  made 
by  Barber  in  1791.  The  Barber  motor  included  an  air  pump  and 
a  compressor  which  forced  the  inflammable  gas  and  air  into  a 
vessel,  where  the  mixture  was  ignited;  the  burning  mixture  issuing 
from  the  vessel  impinged  against  the  vanes  of  a  paddle  wheel  and 
produced  the  rotation  of  a  shaft  connected  to  the  machinery  to  be 
driven.  The  first  reciprocating  engine  using  an  inflammable  gas 
was  invented  by  Street  in  1794. 

Lebon  in  1801  first  suggested  the  compression  of  the  mixture 
of  gas  and  air  before  ignition.  This  was  applied  by  Barnet  in 
1838. 

From  1801  to  1860  many  efforts  were  made  to  produce  a  prac- 
tical internal  combustion  engine.  Several  types  of  free  piston 
engines  were  developed  during  this  pericd  in  which  the  explosion 
of  a  mixture  of  gas  and  air  was  utilized  in  moving  upward  in  a 
vertical  cylinder  a  piston  which  was  free  from  the  connecting 
rod.  The  work  was  done  on  the  return  stroke  by  the  pressure 
of  the  atmosphere  forcing  the  piston  down,  the  piston  rod  on  its 
downward    stroke    producing    rotary   motion    through    a   rack 

191 


192        STEAM  AND  GAS  POWER  ENGINEERING 

meshing  with  a  spur  pinion  and  connected  by  a  ratchet  and  pawl 
to  the  driving  shaft. 

The  Lenoir  engine,  which  was  invented  about  1860,  was  the 
first  internal  combustion  engine  to  be  used  commercially  to  any 
extent  for  producing  power.  The  Lenoir  engine  was  a  horizontal 
double-acting  reciprocating  motor.  The  mixture  of  the  fuel  and 
air  was  drawn  into  one  end  of  the  engine  cylinder  during  the  first 
part  of  the  stroke,  the  inlet  valve  being  closed  at  about  one-half 
of  the  stroke,  when  the  mixture  was  ignited.  The  explosion 
(rapid  combustion)  of  the  mixture  forced  the  piston  to  the  end 
of  the  stroke.  Near  the  end  of  the  stroke  the  exhaust  valve 
opened,  and  the  products  of  combustion  were  expelled  during 
the  return  stroke.  The  same  operation  took  place  at  both  ends 
of  the  cylinder,  the  energy  stored  in  the  flywheel  driving  the 
piston  forward  during  the  suction  part  of  its  stroke.  The 
Lenoir  engine,  similar  to  the  steam  engine,  had  two  working 
strokes  during  each  revolution,  but  was  superseded  by  engines 
working  on  the  Otto  or  Diesel  cycles,  which  have  only  one  work- 
ing stroke  for  every  two  revolutions  of  the  crank  shaft. 

The  Otto  Internal  Combustion  Engine  Cycle. — The  majority 
of  modern  commercial  internal  combustion  engines  operate 
upon  the  Otto  internal  combustion  engine  cycle,  which  was  sug- 
gested by  Beau  de  Rochas  in  1862,  and  which  was  made  a  prac- 
tical success  by  Nicholas  A.  Otto  in  1878.  The  term  engine  cycle 
is  applied  to  the  series  of  events  which  are  essential  for  carrying 
out  the  transformation  of  heat  into  work.  The  Otto  internal 
combustion  engine  cycle  requires  four  strokes  of  the  piston  and 
comprises  five  events,  which  are:  suction,  compression,  igni- 
tion, expansion,  and  exhaust. 

The  action  of  an  internal  combustion  engine  working  on  the 
four-stroke  Otto  cycle  is  illustrated  in  Figs.  158  to  162. 

1.  Suction  of  the  mixture  of  air  and  gas  through  the  inlet  valve 
takes  place  during  the  complete  outward  stroke  of  the  piston, 
the  exhaust  valve  being  closed.  This  stroke  of  the  piston  is 
called  the  suction  stroke  and  is  illustrated  in  Fig.  158. 

2.  On  the  return  of  the  piston,  shown  in  Fig.  159,  both  the  inlet 
and  exhaust  valves  remain  closed  and  the  mixture  is  compressed 
between  the  piston  and  the  closed  end  of  the  cylinder.  This  is 
called   the   compression  stroke.     Just   before   the   compression 


INTERNAL  COMBUSTION  ENGINES 


193 


stroke  of  the  piston  is  completed,  the  compressed  mixture  is 
ignited  by  a  spark  (Fig.  160)  and  rapid  combustion  or  explosion 
takes  place. 

3.  The  increased  pressure  within  the  cylinder  due  to  the  rapid 
combustion  of  the  mixture  drives  the  piston  on  its  second  forward 
stroke,  which  is  the  power  stroke  (Fig.  161).  This  power  stroke, 
or  working  stroke,  is  the  only  stroke  in  the  cycle  during  which 
power  is  generated.  Both  valves  remain  closed  until  the  end 
of  the  power  stroke,  when  the  exhaust  valve  opens  and  provides 
communication  between  the  cylinder  and  the  atmosphere. 


Inlet  Valve.  | 

£s??5a^3__^-*< 

Spark  Plug ■■■>*} 

if  5§ 

@-~~T~~1& 

'xhaust  Valve'  \ 

Suction 

Inlet  Valve-. 
Spark  Plug  ~x 
Exhaust  Valve^ 

Inlet  Valve-. 

I     J 

^■/■/.«#-„.     ^* 

Spark  Plug  ■■■>* 

|J|P^--€2 

Exhaust  Valve" 

Ignition 


Inlet  Valve;, 

Spark  Plug^ 

Exhaust  Valve 


Exhaust 


Expansion 
Figs.   158-162.— The  events  in  the  Otto  Cycle. 


4.  The  exhaust  valve  remains  open  during  the  fourth  stroke 
called  the  exhaust  stroke,  Fig.  162,  during  which  the  burned 
gases  are  driven  out  from  the  cylinder  by  the  return  of  the  piston. 

The  simplest  type  of  internal  combustion  engine  operating  on 
the  Otto  four -stroke  cycle  is  the  gasoline  engine  which  is  illus- 
trated in  Fig.  163.  The  fuel  from  the  liquid  fuel  tank  T  is 
supplied  to  the  mixing  valve  or  carburetor  through  the  fuel 
regulating  valve  G.  The  air,  through  the  air  pipe  A,  enters 
the  same  carburetor  and  is  thoroughly  mixed  with  the  fuel.  The 
mixture  of  air  and  vaporized  fuel  enters  the  engine  cylinder  C 
through  the  inlet  valve  V  as  the  piston  P  moves  on  the  suction 
stroke.  The  mixture  is  then  compressed,  and  ignited  by  an 
electric  spark  produced  at  the  spark  plug  Z,  by  current  fur- 
nished from  the  battery  B.  The  ignition  of  the  mixture  is 
followed  by  the  power  stroke.  The  reciprocating  motion  of  the 
13 


194        STEAM  AND  GAS  POWER  ENGINEERING 


piston  P  is  communicated,  through  the  connecting  rod  R 
to  the  crank  N,  and  is  changed  into  rotary  motion  at  the  crank 
shaft  S.  The  crankshaft  S,  while  driving  the  machinery  to 
which  it  is  connected,  also  turns  the  valve  gear  shaft,  sometimes 
called  the  two-to-one  shaft,  through  the  gears  X  and  Y. 
The  gear  Y  turns  once  for  every  two  revolutions  of  the  crank, 
and  near  the  end  of  the  power  stroke  opens  the  exhaust  valve 
E  through  the  rod  D  pivoted  at  0. 


Fig.  163. — Parts  of  a  gasoline  engine. 

In  larger  engines  the  valve  gear  shaft  also  opens  and  closes 
the  admission  valve  V  and  operates  the  fuel  pump  and  ignition 
system.  As  the  temperatures  resulting  from  the  ignition  of  the 
explosive  mixture  is  usually  over  2000 °F.,  some  method  of 
cooling  the  walls  of  the  cylinder  must  be  used  in  order  to  facili- 
tate lubrication,  to  prevent  the  moving  parts  from  being  twisted 
out  of  shape,  and  to  avoid  the  ignition  of  the  explosive  mixture 
at  the  wrong  time  of  the  cycle.  One  method  of  cooling  gas 
engines  is  to  jacket  the  cylinder  J,  that  is,  to  construct  a 
double-walled  cylinder  and  circulate  water  between  the  two  walls, 
through  the  jacket  space.  The  base  U  supports  the  various 
parts  of  the  engine;  the  flywheel  W  carries  the  engine  through 
the  idle  strokes.  Besides  the  above  details,  every  gas  engine  is 
usually  provided  with  lubricators  L  for  the  cylinder  and  bear- 
ings, and  with  a  governor  for  keeping  the  speed  constant  at 
variable  loads. 


INTERNAL  COMBUSTION  ENGINES 


195 


An  indicator  diagram,  taken  from  a  four-stroke  cycle  internal 
combustion  engine,  using  gasoline  as  fuel,  is  illustrated  in  Fig. 
164.  IB  is  the  suction  stroke,  BC  the  compression  stroke, 
CD  shows  the  ignition  event,  DE  the  power  stroke,  and  EI  is  the 
exhaust  stroke.  The  direction  of  motion  of  the  piston  during 
every  stroke  is  illustrated  in  each  case  by  arrows.  Lines  AF 
and  AG  were  added  to  the  indicator  diagram;  AF  is  the  atmos- 
pheric line,  while  AG  is  the  line  of  pressures.  From  Fig.  164  it 
will  be  noticed  that  part  of  the  suction  stroke  occurs  at  a  pres- 
sure lower  than  atmospheric.  The  reason  for  this  is  that  a 
slight  vacuum  is  created  in  the  cylinder  by  the  piston  moving 
away  from  the  cylinder  head.  The  vacuum  helps  to  draw  the 
mixture  of  fuel  and  air  into  the  cylinder. 


Suction  Stroke 
Fig.  164. — Gas-engine  indicator  card. 

Modern  internal  combustion  engines,  operating  on  the  Otto 
four-stroke  cycle,  will  convert  14  to  30  per  cent,  of  the  heat  avail- 
able in  the  fuel  into  work.  The  Lenoir  engines,  in  which  the 
mixture  was  not  compressed  previous  to  ignition,  converted  only 
about  four  per  cent,  of  the  heat  available  in  the  fuel  into  work. 

The  efficiency  of  engines  operating  on  the  Otto  cycle  depends 
upon  the  pressure  to  which  the  mixture  of  fuel  and  air  is 
compressed  before  ignition.  Theoretically,  the  greater  the  com- 
pression pressure,  the  better  is  the  economy.  Practical  consid- 
erations and  the  danger  of  preignition  limit  the  compression 
pressures  for  various  fuels  to  the  following  values  in  pounds 
per  square  inch:  Gasoline  60  to  90  pounds,  kerosene  50  to  80 
pounds,   alcohol    120   to    180  pounds,  natural    gas   80   to  120 


196        STEAM  AND  GAS  POWER  ENGINEERING 


pounds,  producer  gas   120  to    160   pounds,  blast   furnace  gas 
120    to  190  pounds. 

From  the  above  values  of  practical  compression  pressures  it  is 
evident  that  with  fuels  high  in  hydrocarbons  lower  compression 
pressures  should  be  employed  than  with  fuels  which  are  low  in 
these  constituents. 

The  Two-stroke  Cycle  Engine. — The  internal  combustion 
engine  working  on  the  four-stroke  cycle  requires  two  complete 

revolutions  of  the  crankshaft,  or  four 
strokes  of  the  piston  to  produce  one 
power  stroke.  The  other  three  are  only 
idle  strokes,  but  power  is  required  to 
move  the  piston  through  these  strokes, 
and  this  has  to  be  furnished  by  storing 
extra  momentum  in  heavy  flywheels. 
The  Otto  cycle  can  be  modified  so  that 
the  five  events  can  be  carried  out  during 
only  two  strokes  of  the  piston  by  pre- 
compressing  the  mixture  of  fuel  and 
air  in  a  separate  chamber,  and  by 
having  the  events  of  expansion,  ex- 
haust, and  admission  occur  during  the 
same  stroke  of  the  piston.  In  large 
two-stroke  cycle  engines  the  air  and 
fuel  for  the  mixture  are  compressed  and 
delivered  separately  by  auxiliary  pumps 
driven  from  the  main  engine  shaft, 
the  mixture  in  the  case  of  small  two- 
stroke  cycle  engines  is  accomplished  by  having  a  tightly  closed 
crank  case,  or  by  closing  the  crank  end  of  the  cylinder  and  by 
providing  a  stuffing  box  for  the  piston  rod. 

The  main  features  of  the  two-stroke  cycle  internal  com- 
bustion engine  are  illustrated  in  Fig.  165.  On  the  upward  stroke 
of  the  piston  P,  a  partial  vacuum  is  created  in  the  crank  case  C, 
and  the  explosive  mixture  of  fuel  and  air  is  drawn  in  through  a 
valve  at  A.  At  the  same  time  a  mixture  previously  taken  into 
the  upper  end  of  the  cylinder  W  is  compressed.  Near  the  end  of 
the  compression  stroke,  the  mixture  is  fired  from  a  spark  pro- 
duced at  the  spark  plug  S.     The  explosion  of  the  mixture  drives 


Fig.   165. — Small  two-stroke 
cycle  engine. 


The 


precompression 


of 


INTERNAL  COMBUSTION  ENGINES  197 

the  piston  on  its  downward  or  working  stroke.  The  piston 
descending  compresses  the  mixture  in  the  crank  case  to  about  6 
or  8  pounds  above  atmospheric,  the  admission  valve  at  A  being 
closed  as  soon  as  the  pressure  in  the  crank  case  exceeds  atmos- 
pheric. When  the  piston  is  very  near  the  end  of  its  downward 
stroke,  it  uncovers  the  exhaust  port  at  E  and  allows  the  burned 
gases  to  escape  into  the  atmosphere.  The  piston  continuing  on 
its  downward  stroke  next  uncovers  the  port  at  7,  allowing  the 
slightly  compressed  mixture  in  the  crank  case  C  to  rush  into  the 
working  part  of  the  cylinder  W.  Thus  two  full  strokes  of  the 
piston  complete  one  cycle. 

The  distinctive  feature  of  the  two-stroke  cycle  engine  is  the 
absence  of  valves.  The  transfer  port  I  from  the  crank  case 
C  to  the  working  part  of  the  cylinder  W,  as  well  as  the  exhaust 
port  E,  are  opened  and  closed  by  the  piston. 

Large  two-stroke  cycle  engines  are  often  made  double- 
acting  and  have  the  same  number  of  power  impulses  per  revolu- 
tion as  the  single-cylinder  steam  engine.  The  proper  amounts  of 
gas  and  air  are  delivered  to  each  end  of  the  piston  at  the  correct 
time  by  auxiliary  pumps.  An  admission  valve  is  provided  at 
each  end  of  the  cylinder.  The  exhaust  takes  place  through 
ports  near  the  middle  of  the  cylinder,  which  are  uncovered  by 
the  piston  at  the  end  of  each  working  stroke. 

To  offset  the  advantages  resulting  from  fewer  valves,  less 
weight,  and  greater  frequency  in  working  strokes,  the  two-stroke 
cycle  engine  is  usually  less  economical  in  fuel  consumption  and  is 
not  as  reliable  as  is  the  four-stroke  cycle  engine.  As  the  inlet 
port  I  (Fig.  165)  is  opened  while  the  exhaust  of  the  gases  takes 
place  at  E,  there  is  always  some  chance  that  part  of  the  fresh 
mixture  will  pass  out  through  the  exhaust  port.  Closing  the 
exhaust  port  too  soon  will  cause  a  decrease  in  power  and  effi- 
ciency, on  account  of  the  mixing  of  the  inert  burned  gases  with 
the  fresh  mixture.  By  carefully  proportioning  the  size  and 
location  of  the  ports,  and  by  providing  the  piston  with  a  lip  at 
L  (Fig.  165)  to  direct  the  incoming  mixture  toward  the  cylinder 
head,  the  above  losses  may  be  decreased.  In  large  two-stroke 
cycle  engines  an  effort  is  made  to  eliminate  the  above  loss  by 
forcing  a  current  of  air  through  the  cylinder  by  the  air  pump,  while 
the  exhaust  port  remains  open.     In  any  case  the  scavenging  of 


198        STEAM  AND  GAS  POWER  ENGINEERING 

the  cylinder  of  the  waste  gases  is  not  as  thorough  in  the  two- 
stroke  cycle  as  in  the  four-stroke  cycle  engine,  where  one  com- 
plete stroke  of  the  piston  is  allowed  for  the  removal  of  the  exhaust 
gases.  The  four-stroke  cycle  engine  has  also  the  advantage  of 
wider  use  and  longer  period  of  development. 

The  Diesel  Internal  Combustion  Engine  Cycle. — The  Diesel 
engine  cycle  is  applied  only  to  oil  engines.  This  cycle,  similar 
to  the  Otto,  comprises  five  events:  suction,  compression,  ignition, 
expansion,  and  exhaust.  In  the  Otto  internal  combustion 
engine  cycle,  air  is  mixed  with  the  fuel  in  definite  proportions 
and  the  combustible  mixture  is  subjected  to  the  process  of  com- 
pression. In  the  Diesel  engine  cycle  only  air  is  admitted  to  the 
cylinder  during  the  suction  stroke,  so  that  compression  pressures 
as  high  as  desired  are  permitted  without  the  danger  from  pre- 
ignition.     The  compression  pressures  used  with  Diesel  engines 


Fig.  166. — Indicator  card  from  Diesel  oil  engine. 

vary  from  450  to  500  pounds  per  square  inch.  The  higher 
compression  pressure  limit  in  this  case  is  not  dependent  upon  the 
composition  of  the  mixture  within  the  cylinder  but  upon  con- 
struction details.  At  the  end  of  the  compression  stroke  of  the 
Diesel  engine  piston,  oil  fuel  is  injected  into  the  cylinder.  The 
oil  enters  the  cylinder  in  the  form  of  a  fine  spray,  mixes  with 
the  highly  compressed  air,  which  is  at  a  temperature  of  about 
1000°F.,  is  ignited  and  burns  at  nearly  constant  pressure.  The 
duration  of  the  oil  injection  is  governed  by  the  load  upon  the 
engine.  This  period  of  oil  injection,  as  well  as  the  compression 
pressure,  influences  the  fuel  economy  of  a  Diesel  engine. 

An  indicator  diagram  taken  from  a  Diesel  oil  engine  is  shown 
in  Fig.  166.  Air  is  drawn  into  the  cylinder  during  the  suction 
stroke  A  B.  The  return  of  the  piston  compresses  the  air  to  a 
pressure  of  about  470  pounds  per  square  inch  during  the  stroke 


INTERNAL  COMBUSTION  ENGINES 


199 


BC.     The  fuel-oil  is  then  gradually  introduced  by  means  of  an 
oil  pump,  to  an  amount  depending  upon  the  load,  and  burns 


JQieiSBion  VilTe 


Cooling 
JYater 


Fig.  167. — Cross-section  of  American  Diesel  engine. 

during  CD,  the  first  part  of  the  third  stroke.     This  is  followed 
by  the  expansion  of  the  gases  within  the  cylinder  to  the  end 


200       STEAM  AND  GAS  POWER  ENGINEERING 

of  the  third  stroke  along  DE.  At  E  the  exhaust  valve  opens 
and  the  burned  gases  are  exhausted  from  the  cylinder  during  the 
fourth  stroke  EA . 

A  section  through  a  Diesel  engine  is  illustrated  in  Fig.  167. 
Internal  combustion  engines  operating  on  the  Diesel  cycle  are 
more  expensive  to  build  and  require  better  supervision  than 
engines  operating  on  the  Otto  cycle,  but  give  better  fuel  economy 
and  are  capable  of  operating  with  the  very  cheapest  liquid 
fuels.  Under  good  conditions  Diesel  engines  will  convert 
more  than  30  per  cent,  of  the  heat  in  the  fuel  into  work,  while  oil 
engines  operating  on  the  Otto  cycle  will  usually  convert  only 
about  20  per  cent. 

Details  of  Internal  Combustion  Engines. — The  fundamental 
details  of  an  internal  combuston  engine  are : 

1.  The  Fuel  System. — -This  includes  fuel  storage,  piping  from 
the  storage  to  the  engine,  and  a  device  for  preparing  the  mixture 
of  air  and  fuel.  In  order  to  form  an  explosive  mixture,  air  must 
be  mixed  in  certain  definite  proportions  with  the  fuel,  and  this 
can  be  accomplished  only  when  the  fuel  is  in  the  gaseous  state, 
or  is  a  mist  of  liquid  fuel  easily  vaporized  at  ordinary  tempera- 
tures. Thus  the  essential  difference  between  internal  combus- 
tion engines  using  the  various  fuels  is  in  the  construction  of  the 
device  for  preparing  the  fuel  before  it  enters  the  engine  cylinder. 
If  the  fuel  is  initially  a  gas,  only  a  mixing  valve  is  necessary  to 
control  the  proportions  of  fuel  and  air.  Fuels  which  are  in  the 
liquid  state  must  be  vaporized  and  mixed  with  air  to  form  an 
explosive  charge.  The  devices  required  for  preparing  liquid 
fuels  depend  on  the  character  of  the  fuel,  a  heavy  fuel  requiring 
heat,  while  a  volatile  fuel,  such  as  gasoline,  is  easily  vaporized  at 
ordinary  temperatures  by  being  broken  up  into  fine  mist.  When 
an  engine  uses  a  volatile  liquid  fuel,  like  gasoline,  the  fuel  is 
vaporized  and  mixed  with  the  correct  proportion  of  air  in  a 
device  called  a  carburetor.  Various  types  of  carburetors  will 
be  illustrated  and  explained  in  Chapter  XIII. 

2.  A  Jacketed  Cylinder  and  Piston. — -In  small  engines  only  the 
cylinder  and  cylinder  head  must  be  cooled.  In  large  engines  it 
becomes  necessary  to  cool  also  the  piston  and  the  exhaust  valve 
to  prevent  overheating  of  the  metal.  The  methods  used  in 
cooling  gas  engine  cylinders  are  illustrated  in  Figs.  168  and  169. 


INTERNAL  COMBUSTION  ENGINES 


201 


An  air-cooled  cylinder  is  illustrated  in  Fig.  168.  This  cylinder 
is  cast  with  webs,  and  air  is  circulated  by  means  of  a  fan  driven 
by  the  engine.  The  air  cooling  system  has  not  been  found  prac- 
tical for  stationary  engines  above  5  horsepower,  as  there  is 
no  positive  temperature  control  with  this  system.  This  lack  of 
temperature  control  results  in  the  decomposition  of  the  cylinder 


Fig.  168. — Air-cooled  cylinder. 


oil  and  in  carbon  deposits  on  the  piston  and  cylinder  walls.  t 
Considerable  success  has  been  attained  with  air  cooled  motors 
for  automobiles  and  motorcycles. 

The  cooling  of  engine  cylinder  walls  by  means  of  water  is  the 
most  common  method.  In  this  case  the  cylinder  barrel  or  the 
cylinder  barrel  and  cylinder  head  are  jacketed;  that  is,  they  are 
built  with  double  walls  and  water  is  circulated  through  the  space 


202       STEAM  AND  GAS  POWER  ENGINEERING 


between  the  walls.  The  cylinder  wall  or  barrel  is  cast  separate 
from  the  jacket,  except  in  small  engines,  where  the  cylinder 
barrel  and  jacket  walls  are  cast  together.  In  order  to  definitely 
control  the  temperature  of  the  water  jacket,  the  forced  system 


of  water  circulation  (Fig.  169)  is  generally  used  for  stationary 
engines. 

Cylinders  for  internal  combustion  engines  are  single  acting 
and  are  usually  fastened  to  the  frame  at  one  end  only,  to  allow 
for  the  free  expansion  of  the  metal. 


INTERNAL  COMBUSTION  ENGINES  203 

The  trunk  type  of  piston  (Fig.  169)  is  most  commonly  used, 
for  it  acts  not  only  as  a  piston  but  also  as  a  cross-head.  The 
piston  is  usually  provided  with  three  or  more  rings,  as  it  is  very 
important  that  leakage  past  the  piston  be  eliminated. 

3.  Inlet  and  Exhaust  Valves. — With  the  exception  of  some 
automobile  motors,  which  are  equipped  with  sleeve  valves, 
valves  for  internal  combustion  engines  are  generally  of  the  pop- 
pet or  mushroom  type,  with  conical  seats  (Fig.  169). 

The  inlet  valves  are  not  jacketed,  as  they  are  cooled  by  the 
incoming  mixture  during  the  suction  stroke.  Exhaust  valves 
must  be  cooled  in  all  except  very  small  engines,  as  these  valves 
are  in  contact  with  very  hot  gases  for  a  considerable  period  of 
time. 

Small  engines  are  sometimes  provided  with  inlet  valves  which 
are  automatically  operated  by  the  suction  of  the  piston,  being 
held  to  their  seats  by  weak  springs.  Automatically  operated 
valves  are  uncertain  in  their  action  and  are  seldom  used.  Mechan- 
ically operated  valves  are  positively  controlled  and  are  generally 
used  both  for  inlet  and  for  exhaust  valves. 

The  valves  are  operated  by  means  of  cams  or  eccentrics  from 
an  auxiliary  shaft  which  is  driven  by  means  of  gears  from  the 
main  engine  shaft.  In  the  four-stroke  cycle  engine  the  auxiliary 
shaft  is  operated  at  one-half  the  speed  of  the  main  shaft.  In 
small  engines  the  valves  are  actuated  by  cams,  but  in  large  engines 
eccentrics  are  employed  for  this  purpose. 

4.  A  mechanism  for  changing  the  reciprocating  motion  of  the 
piston  into  rotation  at  the  crank  shaft.  This  change  is  accom- 
plished by  means  of  a  connecting  rod  and  crank. 

5.  Ignition  System. — Ignition  of  the  mixture  in  modern  inter- 
nal combustion  engines  is  accomplished  either  by  a  spark,  or 
automatically  by  the  high  compression  to  which  either  the  air  or 
the  mixture  is  subjected  in  the  engine  cylinder.     The  subject  of  * 
ignition  will  be  treated  in  detail  in  Chapter  XIII. 

6.  A  governor  for  keeping  the  speed  constant  as  the  power 
developed  by  the  engine  varies.  The  governing  mechanism  is 
operated  by  the  speed  variations  of  the  engine  and  the  speed 
control  is  accomplished  either  by  the  hit-or-miss,  or  by  the  throt- 
tling methods  as  will  be  explained  later. 

7.  A  flywheel  for  carrying  the  engine  through  the  idle  strokes. 


204       STEAM  AND  GAS  POWER  ENGINEERING 


8.  Engine  frame  and  bearings  for  supporting  the  various 
parts  of  the  engine. 

9.  Foundations  for  the  engine  and  auxiliaries. 

10.  Lubricating  system  which  includes  grease  cups,  sight- 
feed  oilers,  and  positive  force  feed  oilers.  For  high  speed  motors 
the  forced-flooded  system  of  lubrication  is  commonly  empk^ed. 
In  this  system  a  pump  forces  oil  to  the  various  bearings,  keeping 
them  flooded  with  oil  at  all  times. 

Oil  Engines. — The  first  successful  oil  engines  were  gasoline 
engines,  as  gasoline  is  the  lightest  of  all  commercial  hydrocarbons 


Fig.  170. — Hot-bulb  oil  engine. 

and  is  easily  vaporized  at  ordinary  atmospheric  temperatures. 
Gasoline  engines  consume  one-eighth  to  one-tenth  of  a  gallon  of 
gasoline  per  brake  horsepower  per  hour.  Gasoline  is  the  most 
important  fuel  for  small  stationary  and  portable  engines;  also 
for  light-weight  high  speed  engines,  such  as  are  used  on  auto- 
mobiles and  aeroplanes. 

The  ordinary  gasoline  engines  (Fig.  163)  which  employ  electric 
ignition  cannot  operate  satisfactorily  on  heavy  petroleum  fuels. 
The  type  of  hot  bulb  engine,  illustrated  in  Fig.  170,  has  been  found 
satisfactory  for  petroleum  oils  as  heavy  as  30°  Baum6  (see  Table 
7,  Chapter  XII).  This  engine  is  provided  with  an  un jacketed 
vaporizer  A,  which  communicates  with  the  cylinder  by  means  of 


INTERNAL  COMBUSTION  ENGINES 


205 


the  small  opening  B.  The  vaporizer  is  raised  to  a  red  heat  before 
starting,  by  means  of  a  torch,  and  is  kept  hot  by  repeated  explo- 
sions when  the  engine  is  running.  This  engine  works  on  the 
regular  four-stroke  Otto  gas-engine  cycle.  During  the  suction 
stroke  of  the  piston  only  air  is  sucked  into  the  cylinder  and  the 
charge  of  oil  fuel  is  injected  into  the  vaporizer  by  a  pump.  On 
the  return  stroke  the  air  is  compressed,  forced  into  the  vaporizer, 
mixed  with  the  fuel  and  automatically  ignited.  This  is  followed 
by  the  expansion  and  exhaust  strokes,  as  in  other  internal  com- 
bustion engines. 
A  modification  of  this  type  of  engine  is  the  so-called  semi- 


Fig.  171. — Semi-Diesel  oil  engine. 


Diesel  type  of  oil  engine,  which  can  be  operated  on  the  lowest 
grades  of  petroleum  fuels.  One  type  of  semi-Diesel  engine 
is  illustrated  in  Fig.  171.  Like  the  Diesel,  the  semi-Diesel  engine 
compresses  only  air,  but  operates  at  a  compression  pressure  of 
about  300  pounds  per  square  inch,  depending  partly  on  a  hot 
unjacketed  combustion  chamber  to  ignite  the  charge.  During 
the  suction  stroke  a  charge  of  air  is  drawn  into  the  cylinder, 
which  is  compressed  into  the  combustion  space.  At  or  near  the 
end  of  the  compression  stroke,  the  fuel  oil  is  admitted  in  a  fine 
spray,  is  mixed  with  the  air  and  is  ignited.  The  resulting  expan- 
sion forces  the  piston  on  its  working  stroke.  Near  the  end  of  the 
working  stroke,  the  exhaust  valve  is  opened  and  the  piston  on  its 


206        STEAM  AND  GAS  POWER  ENGINEERING 

return  stroke  expels  the  burnt  charge.     An  indicator  card  from 
a  semi-Diesel  oil  engine  is  illustrated  in  Fig.  172. 

The  Diesel  engine,  previously  described,  is  the  most  economical 
type  of  engine  for  low  grades  of  fuel.  While  its  high  cost  limits 
its  field  of  application  in  small  sizes,  this  is  compensated  in  sizes 
of  100  horsepower  and  greater  by  the  higher  fuel  economy  and 
by  the  ability  of  this  type  to  operate  on  any  liquid  fuel  without 
leaving  an  appreciable  residue.  Recent  tests  indicate  that  Diesel 
engines  will  consume  only  about  0.45  pound  of  low  grade  oil  per 
brake  horsepower  per  hour. 


Fig.  172. — Indicator  card  from  a  semi-Diesel  oil  engine. 

Losses  in  Internal  Combustion  Engines. — Internal  combus- 
tion engines  convert  10  to  30  per  cent,  of  the  heat  energy  supplied 
by  the  fuel  into  useful  mechanical  work.  The  two  greatest 
losses  are  those  due  to  the  heat  carried  away  by  the  jacket  water 
and  by  the  exhaust  gases.  The  loss  in  the  jacket  water  will  vary 
from  25  to  40  per  cent,  of  the  heat  supplied  by  the  fuel.  The  loss 
of  heat  in  the  exhaust  gases,  owing  to  their  high  temperature, 
will  vary  from  25  to  50  per  cent,  of  the  heat  supplied,  increasing 
as  the  jacket  loss  decreases. 

The  other  main  losses  are  those  due  to  incomplete  combustion 
of  the  fuel,  heat  radiated  from  the  outer  surfaces  of  the  engine, 
and  frictional  losses  in  the  mechanism  of  the  engine. 

Installation  and  Care  of  Internal  Combustion  Engines. — The 
general  rules  govering  the  installation  of  steam-power  plant 
equipment  apply  to  internal  combustion  engines.  An  engine 
should  be  installed  in  a  well-lighted  and  ventilated  room,  which 
is  free  from  dirt  and  dust.  The  engine  room  must  be  large  enough 
so  that  there  is  sufficient  space  for  easy  access  to  any  part  of  the 
engine  so  as  to  facilitate  starting,  oiling,  inspection,  and  repair  of 
all  parts. 


INTERNAL  COMBUSTION  ENGINES  207 

In  installing  oil  engines,  the  fuel  tank  should  be  located  outside 
the  building  and  preferably  underground.  In  any  case  the  tank 
should  be  lower  than  the  pipe  to  which  it  is  connected  in  the 
engine  room. 

As  the  mixture  of  fuel  and  air  is  ignited  inside  the  engine 
cylinder,  the  resulting  explosion  produces  a  shock  of  consider- 
able magnitude  on  the  engine  mechanism,  which  in  turn  is  trans- 
mitted to  the  foundation.  This  necessitates  very  carefully  built 
foundations,  which  should  be  separated  from  the  walls  of  the 
building,  so  that  vibrations  caused  by  the  engine  will  not  affect 
the  building  or  the  surrounding  structures. 

The  exhaust  piping  should  be  as  straight  and  as  short  as 
possible  and  the  exhaust  gases  should  discharge  out  of  doors. 
The  air  supply  is  preferably  taken  from  the  outside. 

Betore  an  engine  is  started  for  the  first  time,  all  the  work- 
ing parts  should  be  carefully  examined  and  placed  in  proper 
condition. 

The  gas  engine  is  not  self -starting,  as  is  the  steam  engine  when 
steam  is  turned  on.  The  reason  for  this  is  that  the  explosive 
mixture  of  fuel  and  air  must  be  taken  into  the  cylinder  and 
compressed  before  it  can  give  up  energy  by  explosion.  It  is, 
therefore,  necessary  to  set  the  engine  in  motion  by  some  external 
means  not  employed  in  regular  operation,  before  it  will  pick  up 
its  normal  cycle. 

Small  engines  are  started  by  hand.  This  is  accomplished  by 
turning  the  fly-wheel  over  by  hand  in  the  direction  of  normal 
rotation  until  the  engine  picks  up,  or  by  turning  it  in  opposite 
direction  against  compression  and  then  snapping  the  igniter  by 
hand.  As  it  is  difficult  to  pull  over  an  engine  by  hand  against 
compression  throughout  the  whole  cycle,  some  engines  are  pro- 
vided with  a  starting  cam,  which  can  be  shifted  so  as  to  engage 
the  exhaust  lever.  This  relieves  the  compression  while  crank- 
ing, as  the  exhaust  port  is  open  during  the  first  part  of  the  com- 
pression stroke.  After  the  engine  speeds  up  the  starting  cam  is 
disengaged.  Most  small  engines  and  also  all  engines  for  auto- 
mobiles, tractors,  and  trucks  are  provided  with  starting  cranks. 
Starting  cranks  are  arranged  so  that,  when  turned  in  the  direction 
of  rotation  of  the  engine,  they  grip  the  shaft.  The  starting  crank 
is  released  as  soon  as  the  engine  shaft  turns  faster  than  the  crank. 


208       STEAM  AND  GAS  POWER  ENGINEERING 

As  the  size  of  the  engine  increases  hand  methods  for  starting 
cannot  be  used.  Stationary  gas  and  oil  engines  are  usually 
started  by  compressed  air.  If  the  engine  consists  of  two  or  more 
cylinders,  this  can  be  accomplished  by  shutting  off  the  gas 
supply  to  one  of  the  cylinders  and  running  this  cylinder  with 
compressed  air  from  a  tank,  in  the  same  manner  as  a  steam  engine 
is  operated  with  steam  from  a  boiler.  As  soon  as  the  other 
cylinders  pick  up  their  cycle  of  operations  the  compressed  air  is 
shut  off  and  a  mixture  of  fuel  and  air  is  admitted  to  the  cylinder 
used  in  starting.  With  large  gas  engines  of  only  one  cylinder, 
the  compressed  air  is  admitted  long  enough  to  start  the  engine 
revolving,  when  the  compressed  air  is  shut  off  and  the  mixture  of 
fuel  and  air  is  admitted.  The  air  supply  for  starting  is  kept  in 
tanks  which  are  charged  to  a  pressure  of  50  to  150  lb.  by  a  small 
compressor,  driven  either  from  the  engine  shaft,  or  by  means  of 
an  auxiliary  motor. 

In  electric  central  stations  starting  by  electricity  is  the  simplest. 
Electric  starting  systems  are  also  used  generally  on  modern 
automobiles  as  will  be  explained  in  Chapter  XVI. 

Before  an  internal  combustion  engine  is  started,  the  fuel 
supply  should  be  examined,  the  ignition  system  tested,  the  lubri- 
cating devices  examined  and  placed  in  proper  working  condition, 
the  load  disconnected  from  the  engine,  and  the  spark  mechanism 
retarded  to  the  starting  position.  In  starting  an  engine  by  hand 
cranking,  the  operator  should  always  pull  up  on  the  crank.  As 
soon  as  the  engine  starts,  the  spark  should  be  advanced  to  the 
running  position  and  the  engine  connected  to  its  load. 

To  stop  an  engine,  the  fuel  valve  is  closed,  the  switch  control- 
ling the  ignition  system  is  opened,  the  lubricators  and  oil  cups 
are  closed,  and  the  jacket  water  is  turned  off.  In  cold  weather 
the  water  from  the  engine  jackets  should  be  drained  to  prevent 
freezing.  Before  leaving  the  engine  it  should  be  cleaned,  all 
parts  examined  and  put  in  order  ready  for  starting  up. 

The  operation  and  the  economy  of  an  internal  combustion 
engine  is  greatly  influenced  by  the  proper  timing  of  the  valves 
and  of  the  point  of  ignition.  The  exact  setting  of  the  valves  and 
of  the  point  of  ignition  depends  upon  the  speed  of  the  engine  and 
upon  the  fuel  used. 

The  exhaust  valves  should  open  before  the  end  of  the  power 


INTERNAL  COMBUSTION  ENGINES  209 

stroke  and  generally  from  25°  to  40°  before  the  crank  reaches  the 
outer  or  crank-end  dead  center.  This  is  necessary  to  prevent  loss 
of  power  when  the  piston  starts  on  the  exhaust  stroke.  The  time 
of  opening  of  the  exhaust  valve  must  be  earlier  for  high-speed 
than  for  slow-speed  engines.  The  exhaust  valve  should  remain 
open  until  the  crank  has  turned  5°  to  12°  beyond  the  completion 
of  the  exhaust  stroke.  The  suction  stroke  follows  the  exhaust 
stroke,  and,  in  order  to  prevent  the  mixing  of  the  fresh  charge 
with  the  burnt  gases,  the  inlet  valve  should  open  about  3°  after 
the  exhaust  valve  closes.  The  time  of  closing  of  the  inlet  valve 
should  be  after  the  crank  has  turned  10°  to  25°  beyond  the  comple- 
tion of  the  suction  stroke.  To  ascertain  if  the  valves  of  an 
engine  are  properly  timed,  the  fly-wheel  should  be  turned  over 
slowly  and  the  time  of  opening  and  closing  of  each  valve  noted. 
The  proper  setting  of  the  valves  can  be  accomplished  by  changing 
the  length  of  the  valve  push  rods  or  by  changing  the  timing 
of  the  valve  gear  shaft.  If  for  any  reason  the  gears  are  removed 
on  the  crank  shaft  or  on  the  valve  gear  shaft,  care  should  be 
taken  that  they  are  properly  replaced,  as  one  tooth  out  of  place 
will  throw  the  valve  mechanism  out  of  time. 

The  exact  point  of  ignition 
depends  upon  the  system  of 
ignition,  the  speed  of  the  en- 
gine, the  compression,  and 
upon  the  fuel  used.  Proper 
ignition  timing  can  best  be  de- 
termined by  means  of  an  indi- 
cator. Indicator  cards  show- 
ing early,  late,  and  proper  igni-  FlG-  ^.--Indicator  cards  showing  early, 
.  .  7  x       r-        o  latet  ancj  proper  ignition. 

tion  are  illustrated  in  Fig.  173. 

If  an  engine  runs  well  at  no-load  but  will  not  carry  its  rated 
load,  the  fault  may  be  due  to:  poor  compression,  poor  fuel, 
defective  ignition,  poor  timing  of  ignition,  incorrect  valve  setting, 
incorrect  mixture,  leaky  inlet  or  exhaust  valves,  too  much  fric- 
tion at  bearings,  or  to  the  engine  being  too  small  for  the  rated  load. 

Premature  ignition,  usually  called  preignition,  is  due  to  the 
deposition  of  carbon  or  soot  on  the  walls  of  the  cylinder,  the  com- 
pression being  too  high  for  the  fuel  used;  by  over-heating  of  the 
piston,  exhaust  valve,  or  of  some  poorly  jacketed  part. 


210        STEAM  AND  GAS  POWER  ENGINEERING 

Best  results  will  be  secured  if  the  operation  of  an  engine  is 
placed  in  charge  of  one  man  who  is  held  responsible  for  the  con- 
dition of  the  motor. 

Problems 

1.  Can  an  economical  internal  combustion  engine  be  developed  to  oper- 
ate upon  a  one-stroke  cycle?     Give  reasons  for  your  answer. 

2.  How  does  the  combustion  of  the  mixture  in  an  Otto  cycle  engine  com- 
pare with  the  explosion  of  gunpowder? 

3.  Under  what  conditions  is  the  two-stroke  cycle  engine  most  practical? 

4.  Why  are  higher  compression  pressures  more  practical  with  blast  fur- 
nace gas  than  with  natural  gas. 

5.  At  what  temperature  should  the  water  in  the  jacket  of  a  gas  engine  be 
maintained?     Give  reasons  for  the  temperature  used. 

6.  Compare  poppet  and  slide  valves  for  internal  combustion  engines. 

7.  Why  will  an  automatically  operated  inlet  valve  decrease  the  power  of  a 
gas  engine? 

8.  An  oil  engine  is  found  to  deliver  150  horsepower  when  tested  at  sea 
level.  Will  this  engine  develop  the  same  power  at  Denver,  Colorado? 
Give  reasons  for  your  answer. 

9.  Explain  the  difference  between  preignition  and  backfiring. 

10.  Check  and  correct  the  valve  setting  of  some  internal  combustion 
engine. 

11.  Failure  of  an  internal  combustion  engine  to  start  is  due  to  what 
causes?     Explain  in  detail  causes  and  remedies. 

12.  If  an  internal  combustion  engine  slows  down  and  stops,  apparently 
without  cause,  where  would  you  look  for  trouble?     Explain  in  detail. 

13.  Black  smoke  issues  from  the  exhaust  of  a  gas  engine.  What  is  this  an 
indication  of?     What  causes  blue  smoke  at  the  exhaust? 

14.  What  will  cause  the  deposition  of  carbon  on  the  cylinder  walls? 


CHAPTER  XII 
INTERNAL  COMBUSTION  ENGINE  FUELS  AND  GAS  PRODUCERS 

Fuels 

Classification  of  Fuels. — -Solid,  liquid,  and  gaseous  fuels  are 
used  in  internal  combustion  engines.  The  value  of  a  fuel  de- 
pends upon  its  heating  value,  upon  its  cost,  upon  the  rapidity 
with  which  it  burns,  and  upon  the  cost  of  preparing  it  for  use  in 
the  gas  engine  cylinder.  The  fuel  must  be  capable  of  being 
transformed  into  a  vapor  or  a  gas  before  entering  the  engine 
cylinder,  must  readily  combine  with  air  to  form  an  explosive 
mixture,  and  should  leave  no  residue  or  ash  after  combustion. 

Gaseous  fuels  are  the  simplest  for  use  in  internal  combustion 
engines.  The  fuel  in  the  gaseous  state  requires  simply  a  mixing 
valve  to  proportion  the  air  and  the  fuel  before  the  mixture  enters 
the  engine  cylinder.  For  this  reason  when  a  suitable  gaseous 
fuel  can  be  obtained  at  a  low  cost  it  is  generally  preferred. 

Solid  fuels  in  their  natural  state  cannot  be  used  for  internal 
combustion  engines.  The  chief  difficulty  experienced  in  their 
use  is  from  the  ash  or  residue  which  remains  after  combustion. 
Several  attempts  have  been  made  to  inject  coal  dust  directly  into 
the  cylinder  of  an  internal  combustion  engine,  but  the  resulting 
ash  seriously  interferes  with  the  operation.  Gunpowder  as  a  fuel 
has  also  been  attempted,  but  has  not  proved  successful.  The 
only  successful  method  of  utilizing  the  energy  of  solid  fuels  at  the 
present  time  is  to  transform  the  fuel  from  the  solid  to  the  gaseous 
state.  The  gas  producer,  to  be  explained  later,  is  one  of  the  most 
practical  means  by  which  this  transformation  is  accomplished. 
The  use  of  solid  fuel  requires  considerable  extra  equipment,  but 
has  proved  practical  in  many  instances. 

Liquid  fuels  are  comparatively  inexpensive  in  certain  localities, 
are  easily  transported,  and  large  quantities  of  such  fuels  may  be 
stored  in  a  comparatively  small  space.  Petroleum  distillates 
are  used  most  commonly  in  internal  combustion  engines  al- 

211 


212 


STEAM  AND  GAS  POWER  ENGINEERING 


though  alcohol,  tar,  tar  oil,  shale  oil,  and  phenoloid  (liquid  fuel 
from  blast  furnaces)  are  also  employed  to  some  extent. 

The  Heating  Value  of  a  Fuel. — The  heat  content  of  a  liquid 
or  gaseous  fuel  is  an  important  index  of  its  value,  as  is  the  case 
of  solid  fuels  discussed  in  Chapter  II.  This  property  is  measured 
in  much  the  same  manner  as  is  the  heating  value  of  coal.     The 


Fig.  174. — Gas  Calorimeter. 


fuel  is  burned  in  some  form  of  calorimeter  and  the  heat  liberated 
is  measured  by  the  amount  of  heat  absorbed  by  the  water  which 
surrounds  the  combustion  vessel  or  chamber  of  the  calorimeter. 
In  Fig.  174  is  illustrated  a  calorimeter  for  determining  the  heating 
value  of  gaseous  fuels.  This  type  of  calorimeter  with  special 
equipment  is  also  used  for  testing  light  liquid  fuels. 

The  apparatus  (Fig.  174)  is  designed  for  determining  the  num- 


FUELS  AND  GAS  PRODUCERS  213 

ber  of  heat  units  in  a  certain  volume  of  gas,  as  a  cubic  foot  or  a 
cubic  meter. 

The  gas  enters  the  meter  at  g  and  passes  thence  through  the 
pressure  regulator  to  the  calorimeter  proper,  where  the  gas 
burns  at  the  burner  shown  in  dotted  outline. 

The  products  of  combustion  rise  to  the  top  where  they  enter 
and  pass  down  through  a  double  row  of  pipes  which  are  surrounded 
by  circulating  water  and  leave  at  the  exit  flue  at  the  base. 

The  water  entering  at  a,  passes  through  the  regulating  cock  e, 
thence  around  the  tubes  and  issues  at  c,  whence  it  flows  into  the 
measuring  glass. 

Thermometers  register  the  temperatures  of  the  gases  and  the 
water  entering  and  leaving  the  calorimeter. 

Knowing  the  volume  of  gas  burned,  the  quantity  of  water 
collected,  and  the  temperatures  above  noted,  a  simple  calcula- 
tion gives  the  heating  value  of  the  gas. 

Selection  of  a  Fuel. — -While  the  heating  value  of  a  fuel  is  an 
important  index  of  its  value  several  other  properties  are  usually 
considered. 

The  value  of  a  solid  fuel  depends  upon  the  percentage  of  water 
it  contains,  the  amount  of  ash,  the  tar-forming  ingredients,  and 
whether  it  is  of  a  coking  or  non-coking  variety.  Moisture 
simply  dilutes  the  gas  generated  and  consequently  lowers  its 
heating  value  per  cubic  foot.  A  high  percentage  of  ash  in  the 
fuel  requires  more  frequent  cleaning  of  the  producer  and  often 
causes  a  partial  stoppage  of  the  air  supply.  Coking  fuels  require 
constant  breaking  up  of  the  charge  with  the  consequent  hindrance 
in  the  operation  of  the  producer.  The  formation  of  tar,  which 
results  when  bituminous  or  high  volatile  coals  are  gasified,  re- 
quires cleaning  of  the  gas  before  it  enters  the  gas  engine  cylinder. 
Tar  in  the  cylinder  leaves  a  large  deposit  of  soot,  which  inter- 
feres with  the  operation  of  the  engine.  Anthracite  coal  and  coke 
are  perhaps  the  ideal  solid  fuels  for  gas  producers,  because  of  the 
absence  of  tar,  although  other  varieties  of  coal  and  lignite  are  used 
to  a  certain  extent. 

The  quality  of  a  liquid  fuel  depends  upon  its  specific  gravity, 
flash  point,  water  content,  cold  test,  color,  sulphur  content, 
presence  of  acids,  and  residue. 

By  specific  gravity  is  meant  the  relation  existing  between 


214        STEAM  AND  GAS  POWER  ENGINEERING 


the  weight  of  any  substance  and  the  weight  of  an  equal  volume  or 
bulk  of  water.  The  Baume  hydrometer  (Fig.  175)  is  generally 
used  for  this  determination.  This  instrument  carries  an  arbi- 
trary scale  and  sinks  to  a  depth  corresponding  to  the  density  of 
the  liquid  in  which  it  floats.  Table  7  shows  the  relation  existing 
between  the  Baume*  hydrometer  scale,  the  specific  gravity,  and 
the  weight  of  liquid  fuels  in  pounds  per  gallon. 
Formerly  liquid  fuels  were  judged  mainly  by  their 
I  i  l|J|r  specific   gravity.     In  the  case  of  blended  fuels, 

■]  |  specific  gravity  is  not  an  accurate  indication  of 

its  quality. 

The  flash  point  of  a  liquid  fuel  is  the  lowest 
temperature  at  which  the  vapors  arising  there- 
from will  ignite  when  a  small  test  flame  is  brought 
near  its  surface.  The  flash  point  is  an  index  of 
the  volatile  constituents  of  a  fuel. 

The  cold  test  is  the  lowest  temperature  at 
which  a  liquid  fuel  will  pour.  Upon  this  prop- 
erty depends  the  free  circulation  of  liquid  fuels 
through  pipes. 

Gaseous  fuels  to  be  suitable  for  internal  com- 
bustion engines  must  be  free  from  dust,  tar,  sul- 
phur vapors,  and  other  impurities. 

Distillates  of  Crude  Petroleum. — The  so-called 
distillates  of  crude  petroleum  are  obtained  by 
boiling  or  refining  crude  petroleum,  and  condensing  the  vapors 
which  are  driven  off  at  various  temperatures.  Crude  petroleum 
is  a  mineral  oil  which  is  found  in  greatest  quantities  in  the 
United  States,  Russia,  Mexico,  and  Rumania.  The  exact  com- 
position of  crude  petroleum  varies  in  different  localities.  It  is 
made  up  mainly  of  carbon  and  of  hydrogen,  in  the  ratio  of  about 
two-thirds  carbon  to  one-third  hydrogen.  Crude  petroleum  in 
certain  localities  has  a  paraffin  base;  that  is,  it  yields  a  solid 
paraffin  residue.  Other  petroleums  with  an  asphalt  base  yield 
an  asphalt  residue.  The  specific  gravity  of  petroleum  oils  from 
different  fields  varies  between  0.800  and  0.970. 

The  vapors  which  are  condensed  into  gasoline  are  driven  off 
at  temperatures  of  140  to  160°F.  The  various  grades  of  kero- 
sene are  the  condensed  vapors,  driven  off  at  temperatures  of 


Fig.  175. — Baume 
hydrometer. 


FUELS  AND  GAS  PRODUCERS  215 

Table  7. — Specific  Gravity  and  Baum^  Scale 


Specific 

Degrees 

Pounds  per 

Specific 

Degrees 

Pounds  per 

gravity 

JJaume 

gallon 

gravity 

Baum6 

gallon 

1.000 

10 

8.336 

0.775 

51 

6.462 

0.993 

11 

8.277 

0.771 

52 

6.428 

0.986 

12 

8.220 

0.767 

53 

6.394 

0.979 

13 

8.161 

0.763 

54 

6.358 

0.972 

14 

8.104 

0.759 

55 

6.324 

0.966 

15 

8.051 

0.755 

56 

6.290 

0.959 

16 

7.997 

0.751 

57 

6.258 

0.953 

17 

7.944 

0.747 

58 

6.212 

0.947 

18 

7.891 

0.743 

59 

6.195 

0.940 

19 

7.837 

0.739 

60 

6.163 

0.934 

20 

7.785 

0.736 

61 

6.133 

0.928 

21 

7.736 

0.732 

62 

6.101 

0.922 

22 

7.687 

0.728 

63 

6.070 

0.916 

23 

7.638 

0.724 

64 

6.038 

0.911 

24 

7.590 

0.721 

65 

6.006 

0.905 

25 

7.541 

0.717 

66 

5.975 

0.899 

26 

7.493 

0.713 

67 

5.946 

0.893 

27 

7.444 

0.710 

68 

5.916 

0.887 

28 

7.395 

0.706 

69 

5.886 

0.881 

29 

7.347 

0.703 

70 

5.856 

0.876 

30 

7.298 

0.699 

71 

5.827 

0.870 

31 

7.254 

0.696 

72 

5.797 

0.865 

32 

7.210 

0.692 

73 

5.771 

0.860 

33 

7.166 

0.689 

74 

5.743 

0.854 

34 

7.122 

0.686 

75 

5.715 

0.849 

35 

7.079 

0.682 

76 

5.688 

0.844 

36 

7.038 

0.679 

77 

5.659 

0.840 

37 

6.998 

0.676 

78 

5.632 

0.835 

38 

6.696 

0.672 

79 

5.603 

0.830 

39 

6.918 

0.669 

80 

5.576 

0.825 

40 

6.878 

0.666 

81 

5.548 

0.820 

41 

6.839 

0.662 

82 

5.517 

0.816 

42 

6.804 

0.658 

83 

5.487 

0.811 

43 

6.760 

0.655 

84 

5.457 

0.806 

44 

6.721 

0.651 

85 

5.427 

0.802 

45 

6.683 

0.648 

86 

5.402 

0.797 

46 

6.644 

0.645 

87 

5.374 

0.793 

47 

6.608 

0.642 

88 

5.353 

0.788 

48 

6.571 

0.639 

89 

5.316 

0.784 

49 

6.534 

0.636 

90 

5.304 

0.779 

50 

6.498 

216        STEAM  AND  GAS  POWER  ENGINEERING 

250  to  400°,  and  the  heavy  oils  are  driven  off  at  still  higher 
temperatures. 

Gasoline. — Of  all  petroleum  distillates,  gasoline  is  the  most 
important  fuel  for  automobiles,  airplanes,  and  small  stationary 
and  portable  internal  combustion  engines.  The  consumption  of 
gasoline  has  increased  in  the  United  States  more  than  700  pec 
cent,  during  the  past  ten  years.  The  yield  of  gasoline,  however, 
is  very  small  in  comparison  with  the  heavier  distillates.  By  re- 
fining American  petroleum,  an  average  of  less  than  5  per  cent,  of 
gasoline  is  obtained  and  usually  about  50  per  cent,  of  kerosene. 
This  makes  gasoline  more  expensive  than  other  petroleum  fuels. 

Gasolines  may  be  classified  as:  (1)  straight  refinery,  (2) 
cracked,  (3)  casing  head. 

The  straight  refinery  method  of  manufacturing  gasoline  from 
crude  petroleum  is  to  heat  the  crude  oil  in  a  closed  retort,  called  a 
still,  then  cooling  and  condensing  the  vapors  given  off.  Destruc- 
tive distillation,  or  cracking,  is  prevented  by  keeping  down  the 
temperature  within  the  still  either  by  placing  the  still  under  a 
partial  vacuum  or  by  allowing  steam  to  bubble  through  the  crude 
oil  when  distilling. 

Cracked  gasolines  are  obtained  by  subjecting  petroleum  oils 
of  high  boiling  point  to  high  temperatures  and  pressure;  the 
heavy  oil  decomposes  and  cracked  gasoline  is  recovered  from 
the  distillate. 

Natural  gas  gasoline  is  obtained  from  natural  gas  either  by  the 
compression  or  the  absorption  methods.  The  compression  pro- 
cess is  usually  applied  to  wet  gas,  called  casing  head  gas;  that  is, 
to  gas  which  is  produced  from  the  same  sands  as  petroleum  oil. 
The  absorption  process  can  be  used  with  ordinary  natural  gas. 
A  gasoline  similar  to  casing  head  gasoline  is  also  being  manu- 
factured in  refineries  by  the  compression  process  from  the  very 
light  vapors  which  are  driven  off  when  the  stills  are  first  heated. 

Commercial  gasoline  is  usually  a  physical  blend  of  these 
various  grades.  Its  density  varies  from  57  to  85  degrees  Baume 
(0.65  to  0.75  specific  gravity),  depending  upon  its  composition. 
The  weight  of  gasoline  varies  from  5.4  to  6.2  pounds  per  gallon. 
Its  heating  value  is  about  19,000  B.t.u.  per  pound.  The  flash 
point  ol  gasoline  varies  from  10  to  20°F.  This  means  that  gases 
are  liberated  which  form  an  inflammable  vapor  at  low  tempera- 


FUELS  AND  GAS  PRODUCERS  217 

tures  provided  a  sufficient  supply  of  air  is  present.  For  this 
reason  care  must  be  taken  in  the  handling  of  gasoline.  A  good 
storage  tank  free  from  leaks  and  placed  underground  contributes 
greatly  to  the  safety  as  well  as  to  the  economical  use  of  gasoline. 
When  filling  a  gasoline  storage  tank  or  in  handling  gasoline,  care 
must  be  taken  not  to  have  any  unprotected  flame  nearby.  In 
case  of  fire  it  is  best  to  extinguish  the  flame  by  means  of  wet 
sawdust  or  a  special  fire  extinguisher. 

Kerosene. — Kerosene,  which  can  be  secured  in  greater  quan- 
tities than  gasoline  and  which  has  a  rather  limited  market,  ranks 
next  to  gasoline  among  the  products  of  crude  petroleum  for  use 
in  oil  engines.  Its  density  varies  from  41  to  49  degrees  Baume 
(0.78  to  0.82  specific  gravity).  Its  flash  point  is  70  to  150  de- 
grees depending  upon  the  grade,  and  its  heating  value  per  pound 
is  about  18,500  B.t.u.  Kerosene  is  less  volatile  than  gasoline, 
is  safer  to  handle  and  store,  does  not  evaporate  so  rapidly,  but 
requires  preheating  to  produce  rapid  evaporation.  Kerosene 
is  quite  satisfactory  as  a  fuel  for  engines  operating  under  con- 
stant loads  and  speeds.  Any  gasoline  engine  can  be  operated 
with  kerosene  fuel  provided  it  is  started  and  run  with  gasoline 
until  the  cylinder  walls  become  hot.  Hot  bulb  engines  will  start 
on  kerosene. 

Crude  Oil. — Distillate  and  fuel  oils  are  the  heavier  petroleum 
products  which  are  used  as  fuels  in  Diesel  or  semi-Diesel  types  of 
internal  combustion  engines.  These  fuels  have  a  high  flash 
point  and  a  heating  value  of  18,000  to  20,000  B.t.u.  per  pound. 
The  qualities  of  these  oils  are  based  principally  upon  their  heat- 
ing value  and  to  a  certain  extent  upon  their  specific  gravity. 

Alcohol. — Alcohol  as  a  fuel  for  gas-engine  use  has  many  ad- 
vantages as  compared  with  the  petroleum  distillates.  It  is 
less  dangerous  than  gasoline,  its  products  of  combustion  are 
odorless,  and  it  lends  itself  to  greater  compression  pressures 
than  do  the  various  petroleum  fuels.  Experiments  show  that 
an  engine  designed  to  stand  the  compression  pressures  before 
ignition  most  suitable  for  alcohol  will  develop  about  30  per 
cent,  more  power  than  a  gasoline  engine  of  the  same  size,  stroke, 
and  speed. 

Several  years  ago,  when  the  internal  revenue  tax  was  removed 
from  alcohol,   so   denatured   as  to  destroy  its   character  as  a 


218        STEAM  AND  GAS  POWER  ENGINEERING 

beverage,  it  was  expected  that  denatured  alcohol  would  become 
a  very  important  fuel  for  use  in  gas  engines.  Its  price  up  to  this 
date,  however,  has  been  so  much  higher  than  that  of  gasoline,  the 
most  expensive  of  petroleum  fuels,  that  the  use  of  alcohol  in  gas 
engines  is  out  of  the  question.  It  is  possible  that,  as  the  cost  of 
the  petroleum  distillates  increases,  and  processes  are  developed 
for  producing  denatured  alcohol  at  a  low  price,  the  alcohol 
engine  will  come  into  prominence  as  a  motor. 

American  denatured  alcohol  consists  of  100  volumes  of  ethyl 
(grain)  alcohol,  mixed  with  ten  volumes  of  methyl  (wood)  alcohol, 
and  with  one-half  a  volume  of  benzol. 

The  specific  gravity  of  denatured  alcohol  is  about  0.795  and 
its  calorific  value  is  about  two-thirds  that  of  petroleum  fuels. 
Alcohol  requires  less  air  for  combustion  than  do  petroleum  fuels. 
Theoretically,  the  calorific  value  of  a  cubic  foot  of  explosive 
mixtures  of  alcohol  and  of  gasoline  is  about  the  same.  Actual 
tests  show  that  the  fuel  economy  per  horsepower  is  about  the 
same  for  both  fuels  provided  the  compression  pressures  before 
ignition  are  best  suited  for  the  particular  fuel  used.  In  gasoline 
engines  compression  pressures  of  about  75  lb.  are  used,  while  the 
alcohol  engine  gives  best  results,  as  far  as  economy  and  capacity 
are  concerned,  when  the  compression  pressure  before  ignition  is 
about  180  lb.  per  square  inch. 

Benzol. — -Benzol  is  a  liquid  fuel  derived  from  the  distillation 
of  coal.  In  the  pure  state  it  has  a  density  of  about  29  degrees 
Baume  (0.88  specific  gravity)  and  a  heating  value  of  about  17,200 
B.t.u.  per  pound.  When  mixed  with  various  proportions  of 
gasoline  or  of  alcohol  a  desirable  fuel  results.  A  fifty  per  cent, 
mixture  of  benzol  and  alcohol  has  been  successfully  used  as  a 
fuel.  Commercial  benzol  contains  about  90  per  cent,  benzol 
while  the  remaining  constituents  are  other  minor  coal  tar 
derivatives. 

Shale  Oil. — Shale  oil  is  obtained  from  the  destructive  dis- 
tillation of  shale  in  vertical  retorts  in  which  the  shale  is  exposed 
to  a  temperature  of  about  900°F.  The  crude  shale  oil  has 
a  specific  gravity  of  0.86  to  0.89  and  yields,  by  refining,  oils  which 
are  suitable  for  use  in  internal  combustion  engines  of  special  design. 

Fuel  Gases. — The  fuel  gases  suitable  for  internal  combustion 
engines  are  blast-funace  gas,  coke-oven  gas,  natural  gas,  and 


FUELS  AND  GAS  PRODUCERS  219 

producer  gas.  Internal  combustion  engines  can  also  be  operated 
on  illuminating  gas,  acetylene,  and  oil  gas;  but  these  fuel  gases 
are  usually  too  expensive. 

Illuminating  gas  is  manufactured  by  distillation  of  bituminous 
coal  and  has  a  heating  value  of  about  600  B.t.u.  per  cubic  foot. 

Acetylene  gas  is  formed  when  calcium  carbide  is  decomposed 
by  water  and  has  a  heating  value  of  about  1,500  B.t.u.  per  cubic 
foot. 

Oil  gas  is  produced  by  vaporizing  crude  petroleum. 

Blast-furnace  Gas. — 'Blast-furnace  gas  is  made  by  the  com- 
bustion of  coke  during  the  production  of  pig  iron.  The  gas, 
after  leaving  the  top  of  blast  furnaces,  can  be  purified  and  used 
for  operating  internal  combustion  engines.  Blast  furnace-gas  has 
a  heating  value  of  only  about  100  B.t.u.  per  cubic  foot,  but  can  be 
compressed  to  high  pressures  with  the  resulting  high  efficiency 
if  used  in  internal  combustion  engines  operating  on  the  Otto 
cycle.  From  120,000  to  180,000  cubic  feet  of  blast-furnace  gas 
are  generated  at  the  production  of  each  ton  of  pig-iron,  and  this 
is  available  for  the  generation  of  power  as  well  as  for  the  various 
heating  processes  required  in  the  plant.  Blast-furnace  gas  must 
be  thoroughly  cleaned  of  all  fine  dust  and  of  metallic  vapors 
before  it  is  used  in  gas  engines. 

Coke-oven  Gas. — Coke-oven  gas  has  a  heating  value  of  about 
600  B.t.u.  per  cubic  foot  and  when  free  from  tar  is  suitable  as  a 
fuel  for  internal  combustion  engines.  Modern  coke-oven  plants 
yield  considerable  gas  for  power  purposes,  as  only  about  60  per 
cent,  of  the  gas  generated  in  the  coke  ovens  is  used  as  fuel  for 
the  coking  process. 

Natural  Gas. — Natural  gas  is  found  near  practically  all  oil 
fields  and  has  been  very  successful  as  a  gas  engine  fuel.  The 
heating  value  of  natural  gas  varies  ordinarily  from  900  to  1000 
B.t.u.  per  cubic  foot.  On  account  of  the  high  hydrogen  content 
of  natural  gas,  engines  utilizing  this  fuel  must  operate  at  low 
compression  pressures  in  order  to  prevent  preignition.  Owing 
to  the  need  of  natural  gas  as  a  fuel  for  industrial  and  household 
use  and  to  the  uncertainty  of  a  continued  supply,  its  utilization 
for  the  generation  of  power  is  limited  to  very  few  localities. 

Producer  Gas. — Producer  gas  is  manufactured  from  solid 
fuel  in  a  brick  lined  vessel,  called  a  gas  producer.     The  gas 


220        STEAM  AND  GAS  POWER  ENGINEERING 

producer  is  blown  continously  with  a  mixture  of  air  and  steam, 
in  definite  proportions,  generating  a  combustible  gas,  which  is 
suitable  for  use  in  internal  combustion  engines  or  for  heating. 
Producer  gas  can  be  manufactured  from  charcoal,  coke,  anthra- 
cite coal,  bituminous  coal,  lignite,  peat,  or  wood.  Producers 
operating  on  anthracite  coal  or  coke  have  been  more  satisfactory 
than  those  using  bituminous  coal  or  lignite,  as  anthracite  coal 
producer  gas  contains  very  little  tar  and  the  plant  does  not  have 
to  be  provided  with  elaborate  scrubbing  systems  for  cleaning 
the  gas. 

The  amount  of  gas  generated  per  pound  of  fuel  depends  upon 
the  fuel  used.  Producers  using  lignite  will  usually  generate  less 
than  40  cubic  feet  of  gas  per  pound  of  fuel.  With  bituminous 
coal,  the  gas  generated  per  pound  of  fuel  will  be  about  65  cubic 
feet,  with  anthracite  about  75,  and  with  coke  near  90  cubic  feet 
of  gas  will  be  produced. 

Anthracite  producer  gas  has  an  average  heating  value  of 
about  130  B.t.u.  per  cubic  foot  and  contains  approximately: 
9  per  cent,  of  hydrogen,  24  per  cent,  of  carbon  monoxide,  5  per 
cent,  of  carbon  dioxide,  2  per  cent,  of  hydrocarbons,  and  about 
60  per  cent,  of  nitrogen.  Bituminous  producer  gas  has  a  heat  of 
combustion  of  about  140  B.t.u.  and  contains  approximately: 
12  per  cent,  of  hydrogen,  20  per  cent,  of  carbon  monoxide,  8  per 
cent,  of  carbon  dioxide,  3  per  cent,  of  hydrocarbons,  and  about 
57  per  cent,  of  nitrogen. 

Internal  combustion  engines  using  producer  gas  can  be.  oper- 
ated at  a  compression  pressure  before  ignition  of  about  160 
pounds  per  square  inch  and  will  produce  a  horsepower  for  about 
75  cubic  feet  of  gas,  which  can  be  generated  in  a  producer  by  the 
gasification  of  about  one  pound  of  coal. 

Gas  Producers 

Details  of  Gas  Producers. — -A  gas  producer  is  a  brick-lined 

air-tight  steel  plate  cylinder  arranged  with  a  grate  to  hold  a  thick 

j      bed  of  fuel,  a  hopper  and  an  ash  pit  to  receive  the  fuel  and  the 

I      non-combustible  material  respectively,  means  for  supplying  a 

mixture  of  air  and  steam  to  the  fuel  bed,  a  gas  outlet,  and  gas 

cleaning  apparatus.     Producers  are  usually  provided  with  poke 


FUELS  AND  GAS  PRODUCERS 


221 


holes  and  shaking  grates  for  breaking  up  and  for  maintaining  the 
fuel  bed  in  uniform  condition. 

Details  of  a  typical  producer  generator  are  illustrated  in  Fig. 
176.  Fuel  is  charged  into  the  retort  C  and  is  admitted  to  the 
shell  of  the  generator  by  means  of  a  quick-opening  gate  valve. 
The  retort  C  is  provided  with  a  water-sealed  cover,  this  arrange- 
ment enabling  the  operator  to  charge  the  producer  while  the 
plant  is  in  operation,  without  the  danger  of  admitting  air  or  of 


Water  Seal 


Ooib  Outlet 


>  Green  Fuel  °  - 

e »  Distillation  Zone   • 
'.       700°tol300°F    »> 

„  Dec  omposi  tion  Zone , 
%     About  ldOO°F  p  o 


lAsh  Door 


Fig.   176. — Gas  producer  generator. 


allowing  gas  to  escape.  Coal  entering  the  shell  is  distributed  by 
means  of  the  hood  J',  the  inside  of  which  serves  as  a  gas  collector. 
The  gas  outlet  is  at  J.  A  swinging  grate  Z  supports  the  fuel  bed 
and  is  suspended  from  the  shell  by  chains.  The  shaking  motion 
of  the  grate  is  produced  by  the  hand  lever  L.  Doors  are  provided 
at  the  bottom  for  the  removal  of  ashes.  The  generator  is  provided 
with  peep  holes  and  poke  holes  for  observing  and  maintaining 
the  fuel  bed  in  the  proper  condition.  The  mixture  of  steam  and 
air  enters  at  A.  The  temperatures  of  the  various  zones  are 
approximately  as  indicated  in  Fig.  176. 


222        STEAM  AND  GAS  POWER  ENGINEERING 

Classification  of  Gas  Producers. — Producers  are  classified  by 
the  manner  in  which  the  mixture  of  air  and  steam  is  caused  to 
pass  through  the  producer  and  gas  cleaning  apparatus. 

In  the  suction  types  of  producers  the  air  is  drawn  through  the 
producer  and  gas-cleaning  apparatus  by  the  suction  formed  in  the 
engine  cylinder.  The  rate  of  gas  formation  in  this  type  is 
automatically  controlled  by  the  demand  of  the  engine.  This  type 
of  gas  producer  is  inexpensive  and  is  suitable  only  for  small 
installations. 

In  the  pressure  types  of  producers  the  mixture  of  air  and  steam 
is  forced  through  the  fuel  bed  of  the  producer  by  means  of  a  fan. 
The  amount  of  gas  generated  in  this  case  is  independent  of  the 
amount  used  by  the  engine. 

In  a  third  type,  called  combination  producer,  a  fan  is  placed 
between  the  producer  and  the  engine  which  delivers  the  gas  to  the 
engine  or  to  a  gas  holder  under  pressure.  The  producer  proper 
in  this  case  operates  as  a  suction  producer,  but  the  amount  of  gas 
generated  is  independent  of  the  engine's  demand. 

Gas  producers  are  also  classified  with  reference  to  the  fuel 
gasified.  Anthracite  producers  are  usually  of  the  suction  type, 
the  draft  being  produced  by  the  suction  of  the  engine  piston. 
Bituminous  producers  are  of  the  pressure  or  of  the  combination 
types  and  are  provided  with  special  scrubbers  and  purifiers  for 
removing  tar  and  other  impurities. 

Suction  Gas  Producers. — -A  simple  suction  gas  producer  suit- 
able for  anthracite  coal  is  illustrated  in  Fig.  177.  The  generator 
A  of  the  producer  is  a  cast  iron  or  steel  shell  with  a  grate  below 
and  a  fuel  hopper  above.  Steam  for  the  blast  is  generated  in  a 
vaporizer,  which  is  either  arranged  around  the  top  of  the  pro- 
ducer or  is  independent  of,  but  attached  to,  the  producer  proper. 
The  mixture  of  air  and  steam  enters  at  the  bottom  of  the  fuel 
bed,  a  valve  regulating  the  proportion  of  air  and  steam.  The  gas 
leaving  the  producer  is  cooled  and  purified  in  a  coke-filled  wet 
scrubber  S  and  passes  to  the  engine  cylinder  C. 

In  some  suction  producer  plants  the  gas  is  cooled  and  cleaned 
of  dust  in  a  water-sprayed  coke  scrubber,  after  which  it  is  allowed 
to  pass  through  a  dry  scrubber  on  its  way  to  the  engine.  The 
dry  scrubber  is  filled  with  shavings,  excelsior,  and  iron  turnings 
and  is  intended  to  remove  sulphurous  fumes  from  the  gas. 


FUELS  AND  GAS  PRODUCERS 


223 


The  hand-operated  fan  B  (Fig.  177)  is  used  to  furnish  draft 
during  the  starting  of  the  fires.  When  the  engine  is  in  operation 
the  draft  from  the  fan  B  is  not  necessary.  A  producer  is  also 
provided  with  a  change  valve,  which  is  used  to  discharge  the  poor 
gases  to  the  atmosphere  when  the  fire  is  started  up. 


Fig.  177. — Suction  producer  plant. 


Pressure  Gas  Producers. — One  type  of  pressure  producer, 
called  the  water-bottom  producer,  is  illustrated  in  Fig.  178.  The 
grate  in  this  case  is  dispensed  with  and  the  ashes  drop  into  a 
water  seal  at  the  base  of  the  producer.  The  blast  is  admitted  to 
the  center  of  the  producer  by  a  steam  jet  blower  B.  The  fuel  is 
discharged  from  the  hopper  D  into  the  chamber  E,  from  which  it 
is  distributed  uniformly  by  the  device  F.  Poke  holes  are  pro- 
vided at  G  and  at  H  for  breaking  up  the  fuel  bed.  The  gas 
leaving  the  producer  at  C  enters  scrubbers,  tar  extractors,  and 
other  purifiers  on  its  way  to  the  engine  cylinder.  The  water- 
bottom  type  of  producer  is  advantageous  in  that  the  ashes  can 
be  removed  conveniently  while  the  producer  is  in  operation. 
Some  water-bottom  pressure  producers  are  provided  with  an 
automatic  fuel-feeding  device. 

Combination  Producers. — Combination  producer  plants  have 
a  blower  placed  between  the  producer  and  the  engine  cylinder. 
Some  plants  of  this  type  are  similar  to  the  producers  described 


224        STEAM  AND  GAS  POWER  ENGINEERING 

and  are  equipped  with  elaborate  scrubbers  and  purifiers  when 
operated  with  low  grade  fuels. 

In  the  down-draft  double  furnace  producer,  illustrated  in  Fig. 
179,  the  formation  of  tar  is  prevented  by  carrying  the  gases, 
which  are  distilled  from  the  fresh  fuel  in  the  upper  strata, 
through  the  hottest  zone  at  the  lower  part  of  the  producer. 


Fig.  178. — Pressure  gas  producer. 


The  cleaning  apparatus  used  with  this  type  of  plant  consists  only 
of  a  wet  and  dry  scrubber. 

In  starting  the  down-draft  double  furnace  producer  the  fires 
are  kindled  with  coke  and  wood  in  both  generators  and  the  blower 
is  started,  leaving  open  the  top  doors  H  and  /,  and  valves  A,  B, 
G,  and  C.  Valve  D  is  closed.  As  soon  as  the  fires  are  thoroughly 
kindled,  steam  is  admitted  to  the  top  of  the  generators  at  F  and 


FUELS  AND  GAS  PRODUCERS 


225 


226        STEAM  AND  GAS  POWER  ENGINEERING 

E,  and  mingles  with  the  air  admitted  through  top  doors  H  and  I, 
which  the  operation  of  the  blower  draws  down  through  the  fresh 
charge  of  coal  and  then  through  the  hot  fuel  bed  beneath.  The 
gas  produced  is  then  drawn  down  through  the  grates  and  ash 
pits  of  both  generators,  up  through  the  vertical  boiler,  through 
the  valve  G,  through  the  wet  scrubber,  and  blower.  When  valve 
C  is  closed  and  valve  D  is  opened  the  gas  is  pushed  by  the  blower 
through  the  dry  scrubber  and  to  the  gas  holder.  The  gas  from 
the  gas  holder  is  delivered  to  the  engine  cylinder. 

Rating  of  Gas  Producers. — The  capacity  of  a  gas  producer  is 
expressed  by  the  number  of  pounds  of  fuel  it  can  gasify  per  hour 
or  in  horsepower  if  the  gas  is  generated  for  power  purposes.  The 
gasifying  capacity  of  a  producer  depends  upon  its  design  and 
upon  the  quality  of  the  fuel  used.  The  rating  in  horsepower  is 
incorrect  because  no  mechanical  work  is  done  by  the  producer 
and  there  is  no  definite  relation  between  the  capacity  of  a  pro- 
ducer and  the  power  developed  by  an  internal  combustion  engine. 
There  is  at  present  no  standard  method  for  rating  gas  producers. 

Factors  Influencing  Producer  Operation. — One  of  the  most  im- 
portant factors  to  be  considered  in  the  selection  of  a  gas-producer 
fuel  is  its  volatile  constituents.  The  fuel  that  produces  tar  and 
lampblack  in  large  quantities  will  require  complicated  scrubbing 
systems,  or  producers  of  special  design.  This  will  in  either  case 
increase  the  first  cost  of  the  plant  as  well  as  the  cost  of  the  upkeep 
of  engines  and  pipe  lines.  The  amount  of  tar-forming  gases  is 
small  with  anthracite  coal,  but  is  considerable  in  the  case  of  most 
bituminous  coals  and  lower  grades  of  solid  fuels. 

The  kind  of  ash  is  also  of  importance.  If  the  ash  fuses  or  fluxes 
to  a  clinker,  the  proportion  of  steam  to  air  in  the  blast  must  be 
increased  to  reduce  the  temperature  of  the  fuel  bed.  This  de- 
crease in  temperature  reduces  the  percentage  of  combustible  car- 
bon monoxide  formed  in  the  producer.  The  use  of  too  much 
steam  in  the  producer  results  in  the  formation  of  a  gas  which  has 
considerable  hydrogen.  This  means  that  when  used  in  internal 
combustion  engines  the  gas  cannot  be  compressed  to  as  high  a 
pressure  as  producer  gas  which  has  little  hydrogen. 

Clinker  formation  is  also  serious  because  it  obstructs  the  gas 
passages,  requiring  increased  blast  pressure  to  allow  the  air  to 
pass  through  the  fuel  bed.     Uniform  conditions  during  producer 


FUELS  AND  GAS  PRODUCERS  227 

operation  and  careful  poking  will  reduce  the  difficulties  from 
clinker. 

The  size  of  coal  used  influences  the  capacity  and  efficiency  of  a 
gas  producer.  If  the  coal  is  too  large,  too  little  surface  is  offered 
for  gasification  and  the  producer  efficiency  is  reduced.  A  nut- 
size  of  bituminous  coal  is  best  while  the  pea-size  anthracite  will 
give  good  results.  If  the  coal  is  too  fine,  the  resistance  through 
the  fuel  bed  is  increased,  requiring  greater  blast  pressure,  and 
this  reduces  the  capacity  of  the  producer. 

The  grate  area,  the  rate  of  gasification,  and  the  depth  of  the 
fuel  bed  are  affected  by  the  character  of  the  fuel,  the  lower  grade 
fuels  requiring  a  larger  grate  area,  slower  rates  of  gasification,  and 
deeper  fuel  beds. 

Some  form  of  gas  calorimeter  will  prove  very  useful  in  the  daily 
operation  of  gas  producers. 

Problems 

1.  An  analysis  of  a  gas  by  the  gas  calorimeter  (Fig.  174)  gave  the  follow- 
ing readings:  Gas  passed  through  meter  3  cubic  feet,  water  collected  85 
pounds,  inlet  temperature  65°F.,  outlet  temperature  84°F.  Calculate  the 
heating  value  of  the  gas  in  B.t.u.  per  cubic  foot. 

2.  Compare  the  relative  values  of  gasoline,  kerosene,  alcohol,  and  crude 
petroleum  for  use  in  internal  combustion  engines. 

3.  At  what  price  must  the  ordinary  illuminating  gas  sell  in  order  to  com- 
pete with  natural  gas  at  50  cents  per  thousand  cubic  feet? 

4.  Under  what  conditions  is  the  gas-producer  plant  most  suitable  for 
power  generation? 


CHAPTER  XIII 
AUXILIARIES  FOR  INTERNAL  COMBUSTION  ENGINES 

Carburetors 

Principles  of  Carburetion.— To  successfully  operate  an  internal 
combustion  engine  on  liquid  fuel  it  is  necessary  to  vaporize  the 
fuel  and  mix  it  with  air  in  the  correct  proportions  for  use  in  the 
engine  cylinder.  This  process  of  vaporizing  and  mixing  the  fuel 
with  air  is  known  as  carburetion.  The  function  of  a  carburetor 
is  automatically  to  vaporize  the  liquid  fuel,  and  mix  it  with  air 
in  the  correct  proportions  by  weight  for  use  in  the  engine  cylinder 
and  at  all  speeds  of  the  engine. 

A  mixture  too  rich,  that  is,  having  too  large  a  proportion  of 
gasoline  to  air,  will  give  off  a  black,  odorous  exhaust  due  to  the 
fact  that  some  of  the  gases  are  unburned.  A  mixture  too  lean, 
that  is,  having  insufficient  gasoline,  is  slow  burning  and,  conse- 
quently, may  result  in  back-firing  through  the  carburetor.  A 
lean  mixture  is  accompanied  also  by  the  heating  of  the  motor  and 
by  a  loss  of  power. 

Carburetors. — -Practically  all  modern  carburetors  use  some 
form  of  spray  nozzle  for  vaporizing  the  fuel.  A  throat,  or  Ven- 
turi  tube,  is  usually  made  use  of  to  increase  the  velocity  of  the 
air  at  the  spray  nozzle,  thereby  increasing  the  spray  of  gasoline 
from  the  nozzle. 

Simple  Carburetors  or  Mixer  Valves. — -The  simpler  forms  of 
carburetors  which  are  used  on  stationary  and  constant  speed 
engines  are  called  mixer  valves.  Mixer  valves  are  not  suitable 
for  variable  speed  motors. 

Fig.  180  represents  the  constant  level,  or  overflow  cup,  type 
of  mixer  valve.  B  represents  the  reservoir  in  which  the  constant 
level  of  fuel  is  kept.  A  is  the  supply  pipe.  Gasoline  is  forced 
by  means  of  a  pump,  operated  by  the  engine,  through  the  pipe  A. 
0  is  the  overflow  pipe  the  top  of  which  is  located  just  below  the 

228 


INTERNAL  COMBUSTION  ENGINES 


229 


Fig.  ISO. — Mixer  valve. 


top  of  the  nozzle  Ar.  Air  enters  at  C,  and  on  the  suction  stroke 
of  the  engine  rushes  past  the  nozzle  N,  picking  up  and  mixing 
with  the  spray  of  gasoline  which  is  regulated  by  the  needle  valve 
V.     The  valve  V  is  the  only  adjustment  on  this  mixer  valve. 

Float-feed  Carburetors. — -At  present, 
some  form  of  the  float-feed  type  of  carbu- 
retor is  exclusively  used  on  automobiles, 
trucks,  and  other  variable  speed  motors. 
Float-feed  carburetors  are  of  two  types : 
first,  the  concentric,  in  which  the  float 
chamber  surrounds  the  mixing  chamber, 
or  is  concentric  with  it;  second,  the 
eccentric,  which  has  the  float  chamber 
and  mixing  chamber  side  by  side.  The 
concentric  type  keeps  the  fuel  at  the  pre- 
determined level  much  better  than  the 
eccentric  carburetor.  In  the  concentric 
type,  the  height  of  the  fuel  in  the  nozzle 

is  not  changed  by  road  inclinations,  whereas  in  the  case  of  the 
eccentric  type  the  fuel  level  may  become  very  low  or  may  be 
high  enough  to  actually  flow  from  the  nozzle.  Many  of  the 
successful  modern  carburetors  are  of  eccentric  type,  because 
other  advantages  or  conveniences  more  than  offset  the  disad- 
vantages mentioned  above. 

The  Kingston  Carburetor. — -Fig.  181  represents  a  concentric 
float-feed  type  of  carburetor.  Gasoline  enters  at  G,  flowing 
past  the  valve  V  into  the  float  chamber  W.  The  valve  V  is 
connected  to  the  float  F  by  means  of  a  lever  pivoted  near  its 
center.  When  the  gasoline  reaches  the  correct  level,  the  float 
is  so  set  that  it  closes  the  valve  V  by  means  of  the  lever  men- 
tioned. The  correct  level  of  gasoline  varies  in  different  carbure- 
tors somewhere  between  J^2  and  He  inch  below  the  top  of  the 
spray  nozzle.  Air  enters  the  carburetor  at  A,  passes  downward 
to  the  base  of  the  carburetor,  thence  upward  past  the  spray  nozzle 
J,  where  it  is  mixed  with  the  gasoline.  The  mixing  chamber 
around  J  has  a  reduced  area,  called  the  throat  or  Venturi  tube. 
This  is  arranged  to  increase  the  velocity  of  the  air  at  this  point, 
thereby  producing  more  suction  on  the  gasoline  supply.  S  is  the 
gasoline  adjusting  screw  which  regulates  the  supply  of  gasoline 


230        STEAM  AND  GAS  POWER  ENGINEERING 

by  regulating  the  neeedle  valve  at  J.  Turning  the  screw  S  to 
the  right  decreases  and  turning  to  the  left  increases  the  amount 
of  fuel  used.  The  quantity  of  mixture  used  is  regulated  by  the 
throttle  E. 

As  the  speed  of  the  engine  increases,  the  velocity,  but  not 
the  quantity,  of  the  air  in  the  Venturi  increases  and  the 
suction  on  the  gasoline  becomes  also  greater.  As  a  result 
of  this,  the  actual  supply  of  gasoline  increases,  making  the  mix- 
ture too  rich.  This  is  true  with  any  simple  carburetor, 
and  therefore  some  means  must  be  provided  automatically  to 


Fig.   181. — Kingston  carburetor. 


govern  the  supply  of  gasoline.  Some  carburetors  employ 
auxiliary  air  valves,  other  types  have  compound  nozzles,  while 
several  designs  employ  a  combination  of  nozzles  and  Venturis. 

In  the  Kingston  carburetor  (Fig.  181)  the  desired  result  is 
obtained  by  an  auxiliary  air  valve.  This  is  a  gravity  valve 
consisting  of  several  brass  balls  M  arranged  in  a  semicircle. 
The  balls  are  so  designed  that  when  the  suction  becomes  great 
enough  to  make  the  mixture  too  rich,  the  force  of  gravity  on  the 
balls  will  be  overcome  by  this  suction,  and  they  will  be  lifted 
off  their  seats  thereby  admitting  more  air  into  the  rich  mixture. 
The  auxiliary  air  does  not  pass  the  nozzle  in  this  type  of  carbu- 
retor. The  amount  the  balls  lift  off  their  seats  is  determined 
by  the  suction  resulting  from  the  speed  of  the  engine. 


INTERNAL  COMBUSTION  ENGINES  231 

Marvel  Carburetor. — Fig.  182  represents  a  sectional  view  of 
the  Marvel  carburetor,  which  is  of  the  multiple  jet,  eccentric 
float-feed  type.  There  are  two  spray  nozzles — one  for  low  and 
one  for  high  speeds. 

The  low  speed  nozzle  with  its  throat  is  situated  in  the  un- 
obstructed air  passage.  The  needle  valve  in  this  nozzle  regulates 
the  amount  of  gasoline.  Turning  the  needle  valve  to  right,  or 
up,  makes  the  mixture  leaner  and  to  the  left,  or  down,  makes 


THROTTLE 


Gaso/ine 
Air 


GASOLINE 
ADJUSTMENT 


Fig.  182. — Marvel  carburetor. 

the  mixture  richer.  When  the  speed  of  the  motor  becomes 
great  enough  the  resulting  suction  overcomes  the  force  of  the  air 
valve  spring,  and  the  air  valve  opens,  thereby  cutting  in  the 
high  speed  nozzle  into  the  air  passage. 

The  high  speed  adjustment  consists  of  tightening  or  loosening 
the  tension  on  the  spring,  which  controls  the  air  valve.  For 
a  richer  mixture,  it  would  be  necessary  to  turn  the  air  adjust- 
ment screw  to  the  right  or  clockwise,  and  vice  versa  for  a  leaner 
mixture. 

The  Marvel  carburetor  is  rather  distinctive  in  having  a  hot- 


232        STEAM  AND  GAS  POWER  ENGINEERING 

air  jacket  surrounding  the  mixing  chamber.  Hot-air  is  taken 
off  the  exhaust  manifold  for  heating  the  mixing  chamber,  thereby 
aiding  in  the  vaporization  of  the  fuel.  By  means  of  a  butter-fly 
valve  the  operator  is  able  to  control  the  admission  of  heat  to  the 
hot-air  jacket. 

Stewart  Carburetor. — Fig.  183  represents  a  Stewart  carburetor. 
It  is  of  the  eccentric  type  and  makes  use  of  a  metering  pin  to 


Fig.   183. — Stewart  Carburetor. 

measure  out  the  proper  amount  of  gasoline  for  all  motor  speeds. 
The  gasoline  enters  through  the  strainer  Z  into  the  float  chamber 
C  and  past  the  needle  valve  G.  From  the  float  chamber,  by 
means  of  the  small  passages,  the  fuel  passes  to  the  well  sur- 
rounding the  metering  pin  P  and  into  the  lower  end  of  the 
aspirating  tube. 

At  the  lower  engine  speeds  air  enters  the  combining  tube 
through   the    drilled   passages   H.     In   the   combining   tube   it 


INTERNAL  COMBUSTION  ENGINES 


233 


is  mixed  with  the  vaporized  gasoline  which  has  passed  the  meter- 
ing pin  into  the  aspirating  tube.  The  passages  H  are  open  at 
all  times,  but  the  valve  A  is  held  closed  by  its  weight  until 
opened  by  the  increased  suction  of  the  motor  at  the  higher 
speeds.  As  A  rises  due  to  suction,  the  lower  end  of  tube  is 
less  obstructed  by  the  metering  pin  on  account  of  the  taper  of  the 
pin.  This  larger  opening  then  permits  of  increased  gasoline 
supply  on  the  higher  speeds.     The  taper  of  the  pin  is  such  that 


Throttle  Valve, 


ThrofHe 
,  Shaft- or  Stem 


Large  Venturi- 
Small  Venturi 


Mixture  Control , 
Valve  or  Choker/ 


Idle  Discharge  Jet 

Idle  Adjustment  Needle 

Floe*  t  Needle 


F5W22 


Accelaroitinq  Well- 
Idling  Tube--^ 


■ Floor 


Fig.  184. — Stromberg  plain-tube  carburetor. 

the  proper  amount  of  gasoline  for  all  engine  speeds  is  automat- 
ically taken  care  of. 

The  only  adjustment  is  by  means  of  the  worm  N  and  pinion, 
by  which  the  metering  pin  may  be  lowered  for  increased  gasoline 
supply  and  raised  for  decreased  supply.  For  starting  in  cold 
weather,  it  becomes  necessary  to  increase  the  gasoline  supply  by 
adjusting  the  dash  control.  Usually  the  control  is  left  part  way 
out  until  the  motor  has  become  thoroughly  warmed  up. 

The  Stromberg  Carburetor. — Fig.  184  represents  the  Strom- 
berg plain-tube  carburetor.  A  plain-tube  carburetor  is  one 
in   which  both  the  air  and  the  gasoline  openings  are  fixed  in 


234        STEAM  AND  GAS  POWER  ENGINEERING 


size.  In  this  carburetor  the  proper  proportion  of  air  to  gasoline 
is  maintained  at  all  motor  speeds  by  means  of  what  the  manufac- 
turer calls  an  air  bled  jet.  Air  is  taken  in  through  the  air  bleeder 
and  discharges  into  the  gasoline  channel  before  the  gasoline 
reaches  the  jet  holes  in  the  Venturi.  The  air  enters  the  tube  at 
right  angles  to  the  flow  of  gasoline,  thereby  breaking  up  the  flow 
of  gasoline  and  producing  a  finely  divided  spray.  When  this 
spray  reaches  the  jet  holes  and  is  discharged  into  the  high  velocity 
air  stream,  it  is  further  broken  up  and  enters  as  a  very  finely 
divided  mist. 


COMPENSATOR 

Fig.  185. — Zenith  carburetor. 


Fig.   186. — Holley  carburetor. 


An  accelerating  well  is  made  use  of  to  facilitate  sudden  in- 
creases in  the  speed  of  the  motor. 

The  air  when  the  engine  is  idling  is  drawn  from  below  the 
throttle  and  mixes  with  the  gasoline  before  reaching  the  idling 
jet.  Under  certain  conditions,  the  suction  draws  gasoline  from 
both  idling  jet  and  small  Venturi,  but  as  the  throttle  is  opened 
more,  the  gasoline  comes  only  from  the  Venturi.  The  function 
of  the  large  Venturi  is  to  aid  in  more  finely  dividing  the  gasoline 
vapor  and  further  to  mix  it  in  the  correct  proportion  with  air. 

The  plain-tube  Stromberg  carburetor  has  two  adjustments, 


INTERNAL  COMBUSTION  ENGINES 


235 


one  for  low  and  one  for  high  speeds.  The  low-speed  screw  adjusts 
the  amount  of  air,  and  the  high-speed  screw  regulates  the  quantity 
of  gasoline. 

Zenith  Carburetor. — Fig.  185  represents  a  Zenith  carbure- 
tor, which  is  of  the  eccentric  float-feed  type,  and  makes  use  of  a 
compound  nozzle  to  control  automatically  the  amount  of  gaso- 
line at  all  speeds  of  the  motor. 


Speecf 
Adjustment 


Fig.   187. — Kerosene  carburetor. 


The  Holley  Carburetor. — The  Holley  puddling  type  carburetor 
is  illustrated  in  Fig.  186.  The  gasoline  enters  the  float  chamber 
in  much  the  same  manner  as  in  any  other  carburetor.  From  the 
float  chamber  the  gasoline  passes  to  the  needle  valve.  The  fuel 
level  is  above  the  point  of  the  needle  valve  and,  consequently, 
the  gasoline  rises  above  the  needle  valve,  fills  the  puddle  cup 
C,  and  submerges  the  lower  end  of  the  copper  tube  T.     The 


236        STEAM  AND  GAS  POWER  ENGINEERING 

Holley  carburetor  has  only  one  source  of  air  supply,  there  being 
no  auxiliary  air  valve.  All  the  air  passing  through  the  carburetor 
must  pass  over  the  puddle  of  gasoline  in  cup  C. 

The  needle  valve  N  regulates  the  amount  of  gasoline  supplied 
to  the  well,  and  is  the  only  adjustment  on  this  carburetor. 

Kerosene  Carburetors. — The  Kingston  carburetor  is  used  to 
some  extent  on  engines  operating  with  kerosene.  When  this 
is  done,  there  are  two  separate  and  distinct  carburetors  connected 
by  a  three-way  valve  to  the  intake  manifold.  One  of  the  car- 
buretors is  adjusted  for  gasoline  and  is  used  in  starting;  the  other 
is  adjusted  for  kerosene.  After  the  engine  is  started  and  warmed 
up,  the  three-way  valve  is  turned  and  the  kerosene  carburetor 
is  connected  with  the  intake  manifold. 

Another  form  of  carburetor  for  burning  heavy  fuels  is  illus- 
trated in  Fig.  187.  A  connection  from  the  exhaust  pipe  heats 
the  bowl  of  the  carburetor.  This  heat  is  necessary  in  order  to 
vaporize  the  heavier  fuels.  Above  the  needle  valve  J  is  placed 
a  set  of  stationary  blades  resembling  the  rotor  of  a  windmill. 
The  high  velocity  air  stream  laden  with  particles  of  un vaporized 
kerosene  strikes  these  blades  and  is  given  a  whirling  effect.  This 
throws  the  particles  of  fuel,  due  to  their  inertia,  against  the  sides 
of  the  heated  bowl  and  vaporizes  them  so  that  they  can  be  mixed 
properly  with  the  air  for  use  in  the  cylinder.  This  carburetor 
has  two  needle  valves,  two  adjustments,  as  noted  in  Fig.  187, 
and  also  an  auxiliary  air  valve. 

Ignition  Systems 

For  igniting  the  fuel  charge  in  an  internal  combustion  engine 
two  methods  are  employed:  the  electric  spark,  which  is  most 
commonly  used,  and  the  automatic  ignition  system,  which  is  pro- 
duced by  the  heat  to  which  the  air  or  the  mixture  of  air  and  fuel 
in  the  cylinder  is  subjected. 

In  some  of  the  older  makes  of  engines  the  hot  tube  system  is 
employed.  The  tube,  open  at  one  end  and  closed  at  the  other,  is 
made  of  porcelain  or  of  some  nickel  alloy.  The  closed  end  of  the 
tube  is  heated  by  a  Bunsen  burner.  During  the  compression 
stroke  a  portion  of  the  mixture  is  forced  into  the  tube  and  is 
ignited  by  the  hot  walls.     The  walls  of  the  tube  are  then  kept 


INTERNAL  COMBUSTION  ENGINES  237 

hot  by  heat  caused  from  the  explosions.  Low  first  cost  and  low 
upkeep  are  the  only  points  in  favor  of  this  system,  but  they  are 
more  than  offset  by  the  difficulty  in  regulating  the  time  of 
ignition. 

Electric  Ignition  Systems. — Two  electric  ignition  systems  are 
in  use,  the  make-and-break  and  the  jump-spark.  In  the  case  of 
the  make-and-break  system,  the  spark  is  similar  to  that  pro- 
duced when  one  electric  wire  connected  to  a  battery  is  drawn 
across  another,  or  to  the  spark  produced  by  the  opening  of  a 
switch.  The  spark  in  this  system  is  produced  by  the  contact  and 
quick  separation  of  metallic  points  located  within  the  clearance 
space  of  the  cylinder.  In  the  jump-spark  system,  a  current  of 
high  voltage  is  used  which  jumps  across  a  small  air  gap  within 
the  clearance  space  of  the  cylinder. 

The  Make-and-break  System  of  Ignition. — The  principle  of 
the  make-and-break  system  of  ignition  is  illustrated  in  Fig. 
188.  B  is  the  battery  which  supplies  the  electric  current  for 
ignition.  C  is  an  inductance  spark  coil,  often  called  a  kick  coil. 
It  consists  of  a  bundle  of  soft  iron  wires,  called  the  core,  sur- 
rounded by  many  turns  of  insulated  c 
copper  wire  through  which  the  cur-                               i 

rent  passes.     On  account  of  the  in-         ^ [_ 

ductive  action  of  such  a  coil,  the  spark     //w      T  K_  s 

is    greatly   intensified,    producing    a     ( x°  ) )  Ljj 

strong  arc  from  a  battery  of  low  volt- 
age. S  is  a  stationary  electrode  well 
insulated  from  the  engine,  and  M  a 
movable  electrode  not  insulated  from 


the     engine.     Both     electrodes     are         V*     ^A2A2A2A2A2r-, 

Set    in   the    Combustion    space    of  the      Fig.      188.— Make-and-break 

cylinder.  ignition  systera- 

The  contact  points  of  the  two  electrodes  are  brought  together 
by  means  of  the  cam  T  operated  by  the  valve  gear  shaft  of  the 
engine.  When  the  switch  W  is  closed  current  will  flow  through 
the  circuit  as  soon  as  the  contact  points  of  the  electrodes  are 
brought  together  by  the  cam  T.  A  sudden  breaking  of  the  con- 
tact, aided  by  a  spring,  causes  a  spark  to  pass  between  the  points 
which  ignites  the  mixture.  The  more  rapidly  the  electrodes  are 
separated  the  better  is  the  spark  produced. 


238       STEAM  AND  GAS  POWER  ENGINEERING 

The  contact  between  the  two  electrodes  of  the  make-and- 
break  system  may  also  be  made  by  sliding  one  contact  point  over 
the  other.  This  type  is  known  as  the  wipe-spark  igniter  and  is 
illustrated  in  Fig.  189.     B  is  the  stationary  insulated  electrode 


Fig.  189. — Wipe  spark  igniter. 

and  A  is  the  movable  electrode.  B  is  made  in  the  form  of  a 
spring  and  may  be  moved  toward  the  electrode  A  by  means  of  a 
screw.  The  wiping  action  of  this  igniter  keeps  the  points  clean 
at  all  times. 


Fig.  190. — Hammer-break  igniter. 

Fig.  190  illustrates  the  hammer-break  igniter.  M  is  the 
movable  and  S  the  stationary  insulated  electrode.  The  points 
are  rapidly  separated  by  a  sort  of  hammer  blow  furnished  by  the 


INTERNAL  COMBUSTION  ENGINES 


239 


action  of  the  springs  on  the  end  of  the  movable  electrode.  The 
hammer-break  igniter  is  more  commonly  used  than  the  wipe 
spark  on  account  of  the  easier  adjustment  and  less  wear  of  the 
contact  points. 

The  Jump  Spark  System  of  Ignition. — The  principle  of  the 
jump  spark  system  is  illustrated  in  Fig.  191.  A  is  a  spark  plug, 
the  points  E  and  F  of  which  project  into  the  cylinder.  These 
points  are  stationary,  are  insulated  from  each  other,  and  are 
separated  by  an  air  gap  of  about 
J^2  inch.  When  the  switch  W  is 
closed,  the  current  from  the  bat- 
tery B  flows  through  the  timer  T, 
which  completes  the  circuit  at  the 
proper  time  through  the  induction 
coil  I.  The  induced  high  voltage 
current  produces  a  spark  at  the  Q) 
gap  of  the  spark  plug,  igniting  the 
explosive  mixture  in  the  cylinder. 

The  induction  coil  7,  Fig.  191, 
differs  from  the  inductance  coil 
used  in  connection  with  the  make- 
and-break  system  of  ignition  (Fig. 
188),  in  that  there  are  two  layers 
of  insulated  copper  wire  wound  around  the  soft  wire  core  of  the 
induction  coil,  whereas  in  the  inductance  coil  there  is  only  one 
winding,  the  primary.  The  winding  immediately  surrounding 
the  core  consists  of  several  turns  of  fairly  large  insulated  copper 
wire  and  is  known  as  the  primary  winding.  The  outside  winding 
is  known  as  the  secondary  and  consists  of  a  large  number  of  turns 
of  very  fine  insulated  wire.  It  is  wound  over  the  primary  with- 
out any  metallic  connections.  In  some  cases  a  common  end  or 
terminal  is  used,  in  which  case  this  terminal  is  grounded  thereby 
eliminating  one  ground  wire. 

The  primary  current  must  be  broken  or  interrupted  in  order 
to  induce  a  current  in  the  secondary  winding.  In  the  common 
form  of  induction  coil  this  is  done  by  means  of  vibrator,  some- 
times called  an  interrupter.  The  function  of  the  vibrator  is  to 
break  the  primary  circuit  with  great  rapidity,  thereby  inducing 
a  high  voltage  alternating  current  in  the  secondary  winding. 


Fig.  191. 


-Jump-spaik  ignition 
system. 


240        STEAM  AND  GAS  POWER  ENGINEERING 

This  results  in  a  series  of  sparks  at  the  air  gap  of  the  spark 
plug. 

An  electric  condenser  K  is  made  use  of  to  prevent  the  burning 
of  the  vibrator  points.  It  consists  of  alternate  layers  of  tin-foil 
and  some  insulating  material  such  as  paraffined  paper  and  is 
connected  across  the  vibrator  points.  In  addition  to  preventing 
sparking  at  the  vibrator  points,  the  condenser  absorbs  the  excess 
current  at  the  primary  winding  and  again  gives  it  up  at  the  proper 
time  to  increase  the  intensity  of  the  spark. 

The  induction  coil,  consisting  of  all  the  parts  mentioned,  is 
usually  placed  in  one  box  and  the  space  between  the  parts  is 
filled  with  some  insulating  material  such  as  wax  or  paraffine, 
in  order  to  protect  the  parts  from  moisture. 

In  some  cases  the  primary  circuit  is  broken  by  some  mechanical 
means,  thereby  eliminating  the  vibrator.  One  vibrator,  known 
as  a  master  vibrator,  is  sometimes  used  to  break  the  circuit  for 
several  coils.  In  either  of  the  last  two  cases  mentioned,  the  non- 
vibrator  type  of  induction  coil  is  used. 

The  current  from  the  battery  B  (Fig.  191)  enters 
the  primary  circuit  P  through  the  timer  T  and  the 
vibrator  R.  The  other  end  of  the  primary  is  con- 
nected through  a  ground  with  the  other  terminal 
of  the  battery,  thereby  completing  this  circuit.  As 
the  current  flows  it  magnetizes  the  soft  iron  core  C. 
The  magnetized  core  immediately  attracts  the  steel 
spring  of  the  vibrator  and  thereby  breaks  the 
primary  circuit.  The  core  C  being  of  soft  wire,  it 
immediately  loses  its  magnetism  and  the  spring  R 
is  released  ready  again  to  complete  the  primary  cir- 
cuit. This  vibrating  action  induces  a  high  voltage 
Fig.  19  2.—  current  in  the  secondary  winding  S,  one  end  of 
which  is  connected  to  a  ground  and  the  other  to 
the  center  post  of  the  spark  plug.  The  circuit  is  then  complete 
with  the  exception  of  an  air  gap  of  approximately  >^2  inch  at 
the  spark  plug  points,  across  which  the  current  jumps,  produc- 
ing a  series  of  sparks  which  ignite  the  charge. 

A  spark  plug,  such  as  is  illustrated  in  Fig.  192,  is  used  with  the 
jump  spark  system.  It  consists  of  two  well  insulated  metallic 
points.     The  central  point  is  connected  to  a  binding  post  which 


INTERNAL  COMBUSTION  ENGINES  241 

receives  the  current  from  the  secondary  or  high  tension-  winding 
of  the  induction  coil.  The  other  point  is  about  J^2  inch  distant 
from  the  first  and  is  separated  from  it  by  an  air  gap.  The  second 
point  is  grounded  through  the  thread  of  the  plug  to  the  engine 
frame.  The  insulating  materials  used  in  the  spark  plugs  are 
mica,  porcelain,  and  stone.  The  plugs  are  well  insulated  except 
at  the  air  gap. 

Comparison  of  the  Two  Systems  of  Electric  Ignition. — -The 
jump  spark  system  is  much  more  simple  mechanically,  as  it  has 
no  moving  parts  inside  the  cylinder.  The  make-and-break  sys- 
tem is  more  simple  electrically,  requires  less  care  in  wiring,  does 
not  have  to  be  insulated  so  carefully,  and  the  spark  is  more  cer- 
tain. It  is  difficult  to  lubricate  the  many  parts  of  the  make- 
and-break  system.  The  make-and-break  system  is  usually  used 
on  stationary  slow-speed  engines  and  to  some  extent  on  tractors. 
The  jump  spark  system  is  better  adapted  for  high-speed  and 
multiple  cylinder  engines  than  is  the  make-and-break,  and  is 
used  on  automobiles,  tractors,  trucks,  small  stationary  engines, 
marine  engines,  and  airplanes. 

Source  of  Current  for  Make-and-break,  and  Jump-spark 
Systems. — -The  electric  current  for  producing  the  spark  in  the 
make-and-break  system  may  be  obtained  from  a  primary  battery 
of  dry  or  wet  cells,  from  a  storage  battery,  low  voltage  dynamo,  or 
from  a  low  tension  magneto.  The  current  for  the  jump-spark 
system  may  be  obtained  from  any  of  the  above  sources  or  from 
a  high  tension  magneto.  In  the  latter  case,  the  induction  coil 
is  a  part  of  the  magneto. 

Either  system  requires  a  source  with  about  six  volts  pressure. 
In  case  of  a  battery  this  may  be  obtained  by  connecting  in 
series  4  to  8  dry  cells,  or  3  to  4  storage  battery  cells. 

Electric  Batteries. — Batteries  are  of  two  types — one  type, 
called  the  primary  battery,  generates  electrical  current  by  means 
of  direct  chemical  action  between  certain  substances ;  another  type, 
called  a  secondary  battery,  or  storage  battery,  requires  charging 
with  electricity  from  some  outside  electrical  source  before  it  will 
generate  electrical  energy.  The  active  materials  in  the  primary 
battery  when  once  exhausted  cannot  be  brought  back  to  generate 
electricity  and  must  be  renewed,  while  in  the  storage  battery  the 
active  materials  can  be  used  over  and  over  again. 

16 


242        STEAM  AND  GAS  POWER  ENGINEERING 


The  term  battery  is  applied  to  two  or  more  cells,  whether 
primary  or  storage  types,  when  they  are  connected  together 
to  increase  the  total  amount  of  electrical  energy  delivered  to  a 
circuit. 

Primary  Batteries. — A  primary  cell  (Fig.  1 93)  consists  essen- 
tially of  a  vessel  containing  some  acid  called  the  electrolyte,  in 
which  are  immersed  two  solid  conductors  of  electricity,  called 
electrodes,  one  of  which  is  more  easily  attacked  by  the  acid  than 
x  the  other.     A  simple  cell  consists  of  a  weak 

solution  of  sulphuric  acid,  as  an  electrolyte, 
a  plate  of  zinc,  which  is  easily  decomposed 
by  the  sulphuric  acid,  and  a  plate  of  some 
other  solid  like  copper  or  carbon  which 
resists  the  action  of  sulphuric  acid.  If 
the  plates  of  zinc  and  of  copper  are  put 
side  by  side  in  a  vessel  containing  sulphuric 
acid,  and  the  circuit  is  completed  by  join- 
ing the  two  plates  with  a  wire,  chemical 
action  will  be  set  up  within  the  vessel  or 
cell,  and  a  current  of  electricity  will  be 
^*-— * —  generated. 

Fig.  193.-Wet  primary         The   dry   ^  which   fa  uged   extengively 

at  the  present  time  on  account  of  its 
portability,  is  a  modification  of  the  cell  illustrated  in  Fig. 
193.  It  has  zinc  for  the  negative  electrode,  carbon  for  the 
positive  electrode,  salamoniac  and  zinc  chloride  as  the  elec- 
trolyte for  decomposing  the  zinc,  and  some  oxidizing  agent  like 
manganese  dioxide  to  eliminate  polarization.  The  solution  in 
the  dry  cell  evaporates  slowly,  so  that  it  will  become  worthless 
after  a  time,  even  if  not  used.  Generally  a  dry  cell  in  good  con- 
dition will  have  a  current  strength  of  15  to  25  amperes  and  should 
show  a  pressure  of  134  to  1J^  volts.  A  binding  post  is  attached 
to  the  carbon  and  another  one  to  the  edge  of  the  zinc  cylinder. 

Storage  Batteries. — A  storage  battery  consists  of  two  sets  of 
plates  or  electrodes  known  respectively  as  positive  and  negative, 
submerged  in  a  liquid  called  the  electrolyte.  The  plates  are 
encased  in  a  jar  or  container.  This  type  of  battery  must  be 
charged  frequently  with  electricity,  in  order  that  it  may  con- 
tinue to  give  out  current  to  the  external  circuit.     The  storage 


INTERNAL  COMBUSTION  ENGINES  243 

battery  does  not  store  electricity.  It  stores  energy  in  the  form 
of  chemical  work.  The  electrical  current  produces  chemical 
changes  in  the  battery  and  these  allow  a  current  to  flow  in  the 
opposite  direction  when  the  circuit  is  closed. 

Storage  batteries  are  used  for  gas-engine  ignition  and  are 
preferred  for  this  purpose  to  primary  dry  or  wet  batteries,  on 
account  of  their  greater  capacity  and  more  uniform  voltage. 
Modern  automobiles  also  employ  storage  batteries  for  starting, 
lighting,  and  ignition. 

The  capacity  of  a  storage  battery  is  measured  in  ampere- 
hours,  determined  by  multiplying  the  current  rate  of  discharge 
by  the  number  of  hours  of  discharge  of  which  the  battery  is 
capable  at  that  rate.  As  an  illustration,  a  battery  that  will 
deliver  10  amperes  for  8  hours  has  a  capacity  of  80  ampere-hours. 
The  ampere-hour  capacity  of  a  storage  battery  is  dependent 
upon  the  rate  of  discharge.  Most  manufacturers  specify  the 
rate  of  discharge  for  their  particular  make  of  storage  batteries. 
If  the  rate  of  discharge  is  greater  than  the  specified  amount, 
the  capacity  of  the  battery  is  reduced.  As  an  illustration,  if 
a  storage  battery  has  a  capacity  of  80  ampere-hours,  at  the  10 
ampere  rate,  it  will  have  a  greater  ampere-hour  capacity  if  dis- 
charged at  a  5  ampere  rate;  that  is,  it  will  deliver  a  current  of  5 
amperes  for  more  than  16  hours.  The  normal  rate  of  discharge 
is  the  8  hour  period. 

A  storage  battery  can  be  charged  from  any  direct  current  cir- 
cuit, provided  the  voltage  of  the  charging  circuit  is  greater  than 
that  of  the  storage  battery  when  fully  charged.  Before  a  storage 
battery  is  connected  to  the  charging  circuit  its  polarity  should  be 
carefully  determined,  and  the  positive  and  negative  terminals  of 
the  battery  connected  to  the  positive  and  negative  terminals, 
respectively,  of  the  source.  One  good  method  of  determining  the 
polarity  of  the  wires  from  the  storage  battery  or  source  is  to  im- 
merse them  in  salt  water.  Bubbles  of  gas  will  form  more  rapidly 
on  the  surface  of  the  negative  wire.  Another  test  is  that  the 
negative  wire  will  turn  blue  litmus  paper  red.  Should  the  posi- 
tive wire  of  the  battery  be  connected  to  the  negative  wire  of  the 
source,  the  effect  would  be  a  discharge  of  the  battery,  and  this 
being  assisted  by  the  incoming  current,  a  reversal  of  action  would 
take    place.     This  is  very  injurious  to  the  battery.     It  is  not 


244        STEAM  AND  GAS  POWER  ENGINEERING 


well  to  charge  a  battery  at  too  rapid  a  rate,  as  this  will  raise  its 
temperature  and  will  cause  buckling  of  the  battery  plates.  It 
is  well  also  to  charge  batteries  at  regular  intervals. 

Two  types  of  storage  batteries  are  used — the  lead  storage 
battery  and  the  Edison.  The  Edison  battery  is  also  called  the 
alkaline  or  nickel-iron  battery. 

The  Lead  Storage  Battery.— The  lead  storage  battery,  Fig.  194, 
is  the  type  used  almost  exclusively  in  connection  with  the  modern 

motor  propelled  vehicles.  In  this 
battery  both  the  positive  and  the 
negative  plates  are  built  upon  lead 
grids.  The  perforations  in  the 
positive  grid  are  filled  with  a  lead 
compound  (Pb02)  which  may  be 
distinguished  by  its  brown  color. 
The  perforations  in  the  negative 
grid  are  filled  with  spongy  metallic 
lead  which  has  a  dull  gray  color. 
The  positive  plates  are  all  united  to 
a  common  positive  terminal  and  the 
negative  plates  are  all  united  to  a 
common  negative  terminal. 

A  lead  storage  cell,  when  fully 
charged,  will  show  2.2  to  2.5  volts 
on  open  circuit  and  about  2.15  volts  when  the  circuit  is 
closed.  A  lead  storage  battery  should  not  be  allowed  to  dis- 
charge to  a  voltage  lower  than  1.8  volts  while  giving  its  full  rated 
current.  For  ignition  purposes,  6  and  12  volt  systems  are 
employed. 

For  successful  operation  and  long  life,  storage  batteries  should 
be  tested  frequently  with  a  pocket  volt  meter  for  voltage,  and  with, 
a  hydrometer  for  the  specific  gravity  of  the  electrolyte.  The 
specific  gravity  of  the  electrolyte  of  a  stationary  battery 
should  be  1.17  to  1.22  when  the  battery  is  fully  charged.  A 
portable  battery  should  have  a  greater  specific  gravity, 
from  1.275  to  1.300  when  fully  charged.  Pure  distilled  water 
must  be  added  occasionally  to  the  electrolyte  to  make  up  for 
the  evaporation.  The  electrolyte  should  be  34  to  ^  inch  above 
the  plates. 


Fig.  194. — Cross-section  through 
lead  storage  battery. 


INTERNAL  COMBUSTION  ENGINES 


245 


The  Edison  or  Nickel-iron  Storage  Battery. — The  Edison 
storage  battery,  Fig.  195,  consists  of  two  sets  of  sheet-steel  plates 
or  grids,  submerged  in  an  electrolyte  of  caustic  potash.  The 
plates  or  grids  support  tubes  and  pockets  containing  the  active 
materials.  The  active  materials  on  the  plates  are  nickel  hydrate 
and  a  specially  prepared  black  oxide  of  iron. 


NEGATIVE  POLE-- 

HARD  RUBBER  GLAND: 

CAP 

k<ELL  COVER 


VALVE,    f'f/^R  CAP     G' POSITIVE  POLE 


f- SIDE  ROD 
INSULATOR 


SOLID  STEEL 
CONTAINER 


COPPERWIRE 
■SWEDGED  INTO 
STEEL  LUG 

H  '''CELL  COVER  WELDED 
TO  CONTAINER 

'"STUFFING  BOX 

W-WELD TO  COYER 
J- GLAND  RING 
K-  SPACING  mSHER 
\-- CONNECTING ROD 
M- POSITIVE  GRID 
N-  GRID  SEPARATOR 
0  -SEAMLESS 

■  STEEL  RINGS 
P-  POSITIVE TUBE 
(NICKEL  HYDRATE  8\ 
\NICKEL  IN  LAYERS  ) 


CORRUGATIONS 


SUSPENSION  BOSS 


CELL  BOTTOM-- 
{WELDED  TO  SIDES) 


Fig.   195. — Edison  storage  battery. 


The  plates  are  held  in  a  steel  container  which  eliminates 
the  danger  of  broken  jars.  Hard  rubber  insulation  at  the 
bottom  and  sides  prevents  electrical  contact  between  plates 
and  container. 

Edison  batteries  do  not  have  as  high  capacity  when  new  as 
after  some  weeks  of  use.  This  is  due  to  the  improvement  of 
conditions  in  the  nickel  electrode,  brought  about  by  regular 
charging  and  recharging. 

The  voltage  of  an  Edison  cell,  when  fully  charged,  is  less  than 
2  volts,  which  is  lower  than  in  the  case  of  the  lead  cell.     This 


246       STEAM  AND  GAS  POWER  ENGINEERING 

means  that  more  Edison  cells  will  be  required  for  a  given  voltage 
than  lead  cells. 

Ignition  Dynamos. — An  ignition  dynamo  is  a  miniature  direct- 
current  generator.  It  has  electromagnets  as  field  magnets  and 
is  usually  of  the  iron-clad  type.  One  form  of  ignition  dynamo  is 
shown  in  Fig.  196.  In  using  an  ignition  dynamo  the  internal 
combustion  engine  must  be  started  on  batteries,  as  the  speed 
developed  when  turning  the  engine  by  hand  is  insufficient  to 
produce  a  spark  of  sufficient  intensity  by  the  dynamo.  As  soon 
as  the  engine  speeds  up,  the  battery  current  is  thrown  off  and  the 


Fig.  196. — Ignition  dynamo. 

spark  is  supplied  by  the  ignition  dynamo.  Most  ignition  dyna- 
mos will  supply  a  spark  of  sufficient  intensity  for  a  make-and- 
break  system  of  ignition  without  an  inductance  coil. 

Magnetos. — The  magneto  differs  from  the  ignition  dynamo  in 
that  its  magnetic  fields  are  permanent  magnets.  For  this  reason 
it  is  unnecessary  to  run  the  magneto  for  any  length  of  time  in 
order  to  build  up  its  field.  Magentos  can  be  run  in  any  direction 
and  at  any  speed.  Magnetos  can  be  classed  under  two  general 
heads : 

1.  Low-tension  magnetos  which  are  used  in  place  of  batteries 
or  of  batteries  and  inductance  coils. 

2.  High-tension  magnetos  which  generate  sufficient  voltage  to 
jump  the  gap  of  a  spark  plug. 


INTERNAL  COMBUSTION  ENGINES 


247 


Low-tension  Magnetos. — The  low-tension  magneto  may  be  of 
the  direct-current  type,  in  which  case  it  differs  from  the  ignition 
dynamo  in  that  the  magnetic  field  is  a  permanent  magnet;  or 
may  be  an  alternating-current  magneto.  The  alternating-current 
magnetos  are  generally  used. 

Fig.  197  represents  a  simple  type  of  alternating-current  low 
frequency  magneto.  It  is  used  chiefly  for  the  make-and-break 
system  of  ignition  and  takes  the  place  of  the  battery  and  induc- 
tance coil. 


Fig.  197. — Low-tension  magneto. 


Fig.  198. — Low-tension  magneto 
with  circuit  breaker  and  distrib- 
utor. 


The  magneto  illustrated  in  Fig.  198  is  also  a  low-tension,  al- 
ternating-current magneto,  differing  from  the  preceding  one  in 
that  it  has  a  circuit  breaker  and  a  distributor.  This  magneto  can 
be  used  for  a  jump-spark  ignition  system  when  used  with  a  non- 
vibrating  induction  coil. 

The  distributor  is  made  use  of  in  case  of  multi-cylinder  engines. 
The  function  of  the  distributor  is  to  send  the  current  to  the  right 
cylinder  at  the  proper  time.  The  circuit  breaker,  or  interrupter, 
takes  the  place  of  the  vibrator  in  the  induction  coil  and  mechani- 
cally breaks  the  primary  circuit  thereby  inducing  a  high  voltage 
current  in  the  secondary  circuit.  The  distributor  is  timed  with  the 
circuit  breaker  and  the  circuit  breaker  is  timed  with  the  engine, 
so  that  the  hottest  spark  takes  place  at  the  time  of  ignition. 

Inductor  Type  of  Magneto. — In  all  of  the#magnetos  previously 
mentioned,  the  armature  carried  the  winding  and  has  been  the 


248        STEAM  AND  GAS  POWER  ENGINEERING 

revolving  or  rotating  part.  In  the  inductor  type  of  magneto 
the  winding  and  the  field  magnets  are  stationary  and  the  re- 
volving part,  which  turns  between  the  pole  pieces,  is  made  up 
of  a  steel  shaft  upon  which  are  mounted  laminated  iron  induc- 
tors. By  laminated  parts  are  meant  those  made  up  of  punch - 
ings  of  sheet  iron  placed  side  by  side. 

In  the  inductor  type  of  magneto,  all  moving  wires,  carbon 
brushes,  and  collector  rings  are  eliminated.  It  is  possible  to  have 
inductor  type  of  magnetos  in  connection  with  any  type  of  igni- 
tion on  which  magnetos  are  used.  The  oscillating  magneto  is 
one  of  the  inductor  type  and  is  most  commonly  used  with  the 
make-and-break  system  of  ignition.  This  magneto  gets  its  name 
from  the  fact  that  the  moving  part  does  not  revolve  through  a 
complete  circle,  but  merely  oscillates  through  a  very  few  degrees. 
The  rapid  separation  of  the  points  is  caused  by  strong  springs 
attached  to  the  arms  situated  near  the  end  of  the  rotor  shaft. 
As  the  spring  snaps  the  inductor  back  the  current  is  generated 
and  at  the  same  time  the  igniter  points  within  the  cylinder  are 
very  quickly  separated,  producing  the  spark. 

High-tension  Magnetos. — A  high-tension  magneto  differs 
from  a  low-tension  magneto  in  that  it  can  generate  a  high  voltage 
current  without  the  aid  of  an  induction  coil.  Fig.  199  illustrates 
a  high-tension  magneto  all  the  parts  of  which  are  named.  Both 
the  primary  and  secondary  windings  are  wound  on  the  same  core. 
In  the  armature  type,  both  windings  are  on  the  armature  and 
revolve  with  it,  while  in  the  inductor  type  both  primary  and  sec- 
ondary windings  are  on  the  stationary  coil  between  the  pole  pieces. 

In  the  armature  type,  the  armature  carries  a  primary  winding 
of  a  few  turns  of  fairly  large  insulated  copper  wire  and  a  large 
number  of  turns  of  very  fine  insulated  copper  wire.  The  con- 
denser is  also  carried  in  the  armature.  The  interrupter  or 
circuit  breaker  of  a  high-tension  magneto  is  usually  mounted  on 
the  end  of  the  armature  shaft  and  revolves  with  it.  The 
high-tension  current  is  taken  from  the  armature  by  a  brush  and 
collector  ring.  The  interrupter  also  acts  as  a  timer  and  breaks 
the  primary  circuit  at  the  proper  time.  This  breaking  of  the 
primary  circuit  induces  a  high  voltage  current  in  the  secondary 
exactly  in  the  same  .manner  as  the  vibrator  did  in  the  induction 
coil,  previously  discussed. 


INTERNAL  COMBUSTION  ENGINES 


249 


Due  to  the  fact  that  the  windings  are  revolving,  there  is  a 
generative  as  well  as  an  inductive  effect.  This  generative  effect 
prolongs  the  duration  of  the  spark  which  would  be  of  very  short 
duration  with  the  inductive  effect  alone.  The  cams  must  be 
so  arranged  that  the  primary  is  broken  at  approximately  the  time 
when  the  voltage  is  at  a  maximum,  which  is  when  the  armature 
core  is  removed  from  the  field. 


Longitudinal  Section. 


Rear  View. 


1.  Contact  plate.  8.  Contact  piece.                           14.  Brass  end  cap. 

2.  Slip  ring  with  distributor  segment.  9.  Fastening  screw  for  contact  15.  Flat  spring. 

3.  Carbon.  breaker.                                       16.  Bolt  for  spring  15. 

4.  Carbon  holder.  10.  Timing  lever.                            17.  Condenser. 

5.  Contact-breaker  disc.  11.  Steel  segment.                           18.  Dust  cover. 

6.  Bell-crank  lever.  12.  Sheet-circuiting  screw.           19.  Short  platinum  screw. 

7.  Bell-crank  lever  spring.  13.  Flat  spring  for  timing  lever.  20.  Long  platinum  screw 

Fig.  199. — High-tension  magneto. 


A  safety  gap  is  provided  in  high-»tension  magnetos  to  protect 
the  secondary  winding.  This  is  simply  an  air  gap  across 
which  the  current  may  jump  in  case  of  a  break  in  the  secondary 
winding.  Without  the  safety  gap  the  insulation  of  the  secondary 
would  be  in  danger  of  being  punctured  by  the  high  voltage 
current  in  case  of  a  break  or  loose  connection. 

If  more  than  one  cylinder  is  to  be  served,  a  high-tension  mag- 
neto carries  a  distributor  which  distributes  the  current  to  the 
proper  cylinder. 

Fig.  200  illustrates  a  typical  wiring  diagram  of  a  high-tension 
magneto  of  the  armature  type. 

Timer  and  Distributor  Systems. — With  multiple  cylinder 
engines  a  timer  is  often  used  in  connection  with  vibrating  indue- 


250        STEAM  AND  GAS  POWER  ENGINEERING 


tion  coils.  The  function  of  the  timer  is  to  complete  the  primary 
circuit  at  the  proper  time  for  each  cylinder  thereby  causing  the 
vibrator  to  function  resulting  in  a  hot  spark  at  the  spark  plug. 


Condenser 
Fig.  200. — Wiring  diagram  for  a  high-tension  magneto. 

One  type  of  timer,  illustrated  in  Fig.  201,  is  used  on  a  four-cylin- 
der engine.     E  represents  the  segments  in  the  housing  S.     These 


Fig.  201. — Timer. 

segments  are  electrically  insulated  from  each  other  with  fibre 
or  some  other  insulating  material.  R  is  the  revolving  arm  for 
closing  the  circuit  at  the  proper  time. 


INTERNAL  COMBUSTION  ENGINES 


251 


The  distributor  system  of  ignition  is  very  common  practice  on 
multiple  cylinder  high-speed  engines.  In  this  system  the  dis- 
tributor and  circuit  breaker  are  mounted  on  one  shaft.  This 
shaft  has  projections  or  in  some  cases  indentations  equally  spaced 
and  corresponding  to  the  number  of  cylinders  to  be  served. 
These  projections  or  indentations  act  as  cams  for  interrupting 
the  primary  circuit.  A  condenser  is  usually  placed  across  the 
breaker  points  to  prevent  sparking  at  the  points.  In  connection 
with  this  system  a  non-vibrating  induction  coil  is  usually  used. 
One  end  of  the  secondary  is  usually  grounded,  while  the  other 


._  &£ounof± L-L-JL-JUJ 

Fig.  202. — High-tension  distributor  system. 

leads  to  the  center  post  of  the  distributor.  The  distributor 
then  conducts  the  secondary  to  the  proper  cylinder  at  the  proper 
time. 

Fig.  202  represents  a  high-tension  distributor  system  em- 
ploying a  timer  and  vibrating  induction  coil. 

In  most  distributor  systems  a  circuit  breaker  takes  the  place 
of  both  timer  and  vibrator  so  that  a  non-vibrating  induction  coil 
can  be  used. 

Governors 

Every  internal  combustion  engine  must  be  provided  with  a 
governor  in  order  that  its  speed  may  be  kept  constant  as  the 
power  developed  by  the  engine  varies.     Stationary  engines  are 


252        STEAM  AND  GAS  POWER  ENGINEERING 

usually  mechanically  regulated,  the  governor  being  operated  by 
the  speed  variations  of  the  engine.  Motor  vehicles  are  generally 
hand-governed,  but  are  often  equipped  with  a  limit  governor 
to  prevent  overspeeding.  The  speed  regulation  of  internal  com- 
bustion engines  is  accomplished  by  one  of  the  following  methods : 
hit-and-miss  system,  varying  the  quality  of  the  mixture,  varying 
the  quantity  of  the  mixture,  varying  the  time  of  ignition,  and 
combination  systems. 

Hit-and-miss  Governing. — In  this  system  the  number  of  explo- 
sions is  varied  according  to  the  load  of  the  engine.  When  the 
engine  is  running  at  full  load  the  explosions  follow  each  other  in 
regular  order  until  the  speed  has  increased  enough  above  the 
normal  to  cause  the  governor  to  act,  preventing  the  drawing  in 
of  the  next  charge,  thus  missing  an  explosion.  This  is  followed 
by  the  slowing  down  of  the  engine,  which  causes  the  explosions 
to  recur. 

The  hit-and-miss  system  can  be  carried  out  in  several  ways  de- 
pending upon  the  valve  gear  of  the  engine. 

In  the  case  of  small  engines,  where  the  inlet  valve  is  operated 
automatically  by  the  suction  of  the  piston,  the  governor  acts  by 
keeping  the  exhaust  valve  open,  thus  preventing  the  spring-loaded 
inlet  valve  from  opening. 

When  the  inlet  valve  is  mechanically  operated  from  the  valve 
gear  shaft,  the  governor  acts  directly  on  the  inlet  valve  by  with- 
drawing a  trigger,  called  a  pick-blade,  or  a  cam-roller  in  the  valve 
actuating  mechanism,  thus  preventing  the  admission  of  a  new 
charge  at  light  loads. 

The  hit-and-miss  system  can  also  be  operated  by  keeping  the 
fuel  valve  closed  so  that  the  engine  draws  in  only  air  at  light  loads. 

The  governor  proper  in  connection  with  the  hit-and-miss  sys- 
tem is  usually  some  form  of  fly-ball  governor. 

The  hit-and-miss  system  of  governing  is  very  simple  and  gives 
good  fuel  economy  at  variable  loads.  As  the  explosions  in  the 
engine  cylinder  do  not  occur  at  regular  intervals,  this  system  of 
governing  necessitates  the  use  of  very  heavy  fly-wheels  in  order 
to  keep  the  speed  .fluctuations  within  practical  limits.  The  hit- 
and-miss  system  is  satisfactory  for  small  engines  where  close 
speed  regulation  is  not  essential,  but  is  not  practical  in  connection 
with  engines  which  must  operate  at  nearly  constant  speed. 


INTERNAL  COMBUSTION  ENGINES  253 

Quality  Governing. — In  this  system  the  number  of  explosions 
per  minute  and  the  quantity  of  the  mixture  admitted  to  the 
cylinder  remain  constant,  but  the  quality  of  the  mixture,  that  is, 
the  ratio  of  fuel  to  air,  is  varied  according  to  the  load.  This  is 
accomplished  either  by  the  governor  controlling  a  throttle  or  a 
cut-off  valve  in  the  gas  supply  pipe.  The  inlet  valve  which  ad- 
mits the  mixture  to  the  engine  cylinder  opens  under  all  load  con- 
ditions to  its  full  lift,  admitting  to  the  cylinder  a  mixture  of  the 
same  volume  at  different  loads.  The  governor  controls  both  the 
air  and  gas  openings,  increasing  the  air  supply  at  light  loads  in  the 
same  proportion  as  the  amount  of  gas  is  decreased. 

This  method  of  governing  retains  the  same  compression  pres- 
sure at  all  loads,  but  the  fuel  economy  decreases  very  rapidly  as 
the  load  drops,  as  weak  mixtures  are  difficult  to  ignite  and  are 
slow  burning. 

Quantity  Governing. — In  the  quantity  governing  system  the 
proportion  of  air  to  fuel  remains  constant,  but  the  speed  regula- 
tion is  accomplished  by  altering  the  quantity  of  the  charge  admit- 
ted to  the  cylinder  at  variable  loads.  This  system  of  governing 
can  be  carried  out  by  the  use  of  a  butterfly  valve  under  the  control 
of  the  governor,  which  throttles  the  charge  in  a  manner  similar 
to  the  throttling  steam  engine.  By  another  method,  call- 
ed the  cut-off  method,  the  inlet  valve  is  held  open  only  during 
a  portion  of  the  suction  stroke,  and  is  suddenly  closed  at  a  point 
determined  by  the  governor  and  suitable  to  the  load.  The  cut- 
off method  of  quantity  governing  is  similar  in  its  action  to  the 
governor  in  connection  with  automatic  cut-off  steam  engines, 
such  as  the  Corliss. 

Combination  Systems. — A  combination  of  the  hit-and-miss  and 
the  throttling  regulating  systems  has  been  tried.  The  throttling 
constant  quantity  system  is  used  for  loads  above  one-half  the 
rated  load  of  the  engine,  whereas  the  hit-and-miss  system  is  em- 
ployed for  loads  below  one-half.  Another  combination  governor 
uses  quality  governing  at  heavy  loads  and  quantity  governing  at 
light  loads.  These  combination  systems  have  been  designed  to 
utilize  the  advantages  of  the  several  systems,  but  are  complicated 
and  are  used  only  in  special  cases. 


254       STEAM  AND  GAS  POWER  ENGINEERING 


Mufflers 

An  exhaust  muffler  is  generally  used  to  silence  the  noise  inci- 
dental to  the  escape  into  the  air  of  the  exhaust  gases  from  an 
internal  combustion  engine.  In  some  installations  mufflers  are 
also  used  for  the  air  intakes  of  large  engines. 

Exhaust  mufflers  vary  greatly  in  design,  but  are  intended  to 
silence  the  exhaust  noise  by  reducing  the  velocity  of  the  exhaust 
gases  to  a  minimum,  without  appreciably  increasing  the  back 
pressure. 

In  some  cases,  the  muffler  is  an  enlarged  exhaust  pipe  or  a  vessel 
of  suitable  volume  to  permit  the  gradual  expansion  of  the  exhaust 
gases.  Some  mufflers  are  provided  with  baffles  and  other  ob- 
structions to  reduce  the  velocity  of  the  exhaust  gases.  In  other 
cases,  sprays  of  water  have  been  employed  in  connection  with 
mufflers,  to  reduce  the  velocity  of  the  gases  by  cooling.  The 
use  of  water  is  effective,  but  should  not  be  employed  if  the  exhaust 
gases  contain  sulphur  compounds. 

A  muffler  should  have  sufficient  volume  in  order  to  throw  little 
back  pressure  on  the  engine,  should  be  strong  enough  to  stand  the 
strain  of  an  explosion,  which  may  result  from  the  presence  of 
unburned  gases  in  the  exhaust,  and  should  be  constructed  so  that 
it  can  be  readily  taken  apart  for  inspection,  cleaning  and  repair. 

The  exhaust  gases  from  an  internal  combustion  engine  should 
never  be  allowed  to  escape  into  a  chimney  or  into  a  sewer,  as  an 
explosion  due  to  the  accumulation  of  unburned  gases  may  occur 
at  any  time. 

Problems 

1.  Examine  some  float  feed  carburetor  and  hand  in  report  showing  how 
these  carburetors  differ  from  those  described  in  the  text.  Clear  sketches, 
showing  fundamental  details  of  construction,  should  accompany  report. 

2.  Examine  some  magneto  and  hand  in  a  report  which  will  illustrate  and 
explain  its  construction. 

3.  Show  by  means  of  clear  sketches  the  details  of  a  hit-and-miss  governor 
and  also  of  a  governor  of  the  throttling  type. 

4.  Examine  the  lubricators  in  use  on  various  stationary  internal  combus- 
tion engines  and  report  in  which  respects  these  differ  from  lubricators  for 
steam  engines. 

5.  Make  clear  sketches  of  mufflers  suitable  for  small  and  for  large  station- 
ary internal  combustion  engines. 


CHAPTER  XIV 
GAS  POWER  PLANT  TESTING 

The  testing  of  internal  combustion  engines  operating  upon 
gaseous  or  liquid  fuels  is  similar  to  the  testing  of  steam  engines, 
at  least  in  the  more  important  details.  The  heat  supplied  to  the 
engine  by  the  fuel  and  the  delivered  power  are  the  two  main 
points  to  be  investigated.  Indicators  cards  may  be  used  to 
determine  the  inner  workings  of  the  cylinder  and  in  measuring 
the  indicated  horse  power.  The  amount  of  heat  absorbed  by 
the  jacket  water  can  be  determined  by  weighing  the  amount  of 
water  passing  through  the  jacket  and  taking  the  temperature 
of  the  inlet  and  outlet  water. 

Measurement  of  Fuel  Used. — When  the  fuel  used  is  in  a 
gaseous  state,  the  volume  used  is  usually  measured  by  some  form 
of  gas  meter.  Most  commercial  meters  give  a  fair  degree  of 
accuracy,  but  they  should  be  calibrated  under  the  conditions  to 
which  they  are  subjected  during  the  test.  Venturi  meters 
(Chapter  X)  are  used  when  the  volume  of  the  gas  to  be  measured 
is  large. 

When  liquid  fuels  are  used  the  amount  supplied  the  engine 
is  best  measured  by  means  of  small  platform  scales.  One  method 
consists  in  placing  a  supply  tank  or  reservoir  upon  the  scales, 
using  a  flexible  connection  from  the  tank  to  the  carburetor.  The 
difference  in  the  weight  of  the  fuel  at  the  beginning  and  at  the 
end  of  the  test  gives  a  direct  measure  of  the  quantity  of  fuel  used. 
The  flexible  connection  between  the  tank  and  engine  is  best  made 
of  flexible  metallic  tubing  having  no  rubber  insertions.  Rubber 
tubing  is  acted  upon  by  petroleum  fuels  and  is  soon  destroyed. 

Many  internal  combustion  engines  are  equipped  with  an  over- 
flow type  of  carburetor,  in  which  a  constant  quantity  of  fuel  is 
maintained  in  the  carburetor  by  supplying  a  larger  quantity  of 
fuel  than  is  necessary,  while  the  excess  is  drained  through  an 
overflow  pipe.  In  this  case  the  method  of  weighing  the  fuel  is 
much  the  same  as  that  just  explained,  with  the  exception  that  the 

255 


256        STEAM  AND  GAS  POWER  ENGINEERING 

fuel  from  the  overflow  is  collected  in  a  separate  vessel  and  is 
either  returned  to  the  main  fuel  tank  before  the  final  weighing  at 
the  end  of  the  test  or  is  weighed  separately  and  the  amount 
deducted  from  the  weight  as  determined  from  the  main  tank. 

Instead  of  measuring  the  fuel  by  weighing,  measurements  by 
volume  are  sometimes  used.  In  that  case  a  cylindrical  vessel  of 
small  diameter  is  equipped  with  a  gage  glass.  The  vessel  is 
calibrated  by  filling  the  tank  to  various  heighths  and  by  deter- 
mining the  corresponding  weight  of  fuel  per  inch  of  height.  The 
fuel  supplied  to  the  engine  during  the  test  is  then  indirectly 
measured  by  noting  the  difference  of  the  fuel  level  in  inches  and 
converting  it  into  pounds  from  the  calibration  data.  Such  a 
method  is  not  considered  accurate  because  of  the  change  of 
volume  of  the  fuel  with  the  change  of  temperature.  For  accurate 
results  the  method  of  direct  weights  should  be  used. 

Heat  Consumption  of  the  Engine. — The  heat  consumption  of 
the  engine,  or  the  heat  supplied  by  the  fuel,  is  found  in  the  case  of 
gaseous  fuels  by  multiplying  the  heat  of  combustion  of  one  cubic 
foot  of  the  fuel,  as  determined  by  calorimeter  test,  by  the  volume 
of  the  gas  consumed  in  cubic  feet.  For  liquid  fuels  the  heat 
consumption  is  equal  to  B.t.u.  per  pound  of  fuel  multiplied  by  the 
weight  of  fuel  used  in  pounds. 

Brake  Horsepower. — The  brake  horsepower,  or  the  delivered 
horse  power,  of  an  internal  combustion  engine  is  usually  measured 
by  means  of  a  Prony  brake.  Other  types  of  dynamometers,  as 
explained  in  the  measurement  of  the  delivered  power  of  the  steam 
engine  (Chapter  X),  could  also  be  used. 

When  a  Prony  brake  is  used  the  power  is  calculated  by  the 
formula: 

-r.  ,  2-n-lwn 

Rhp-  =  33000 

In  which  t  =  3.1416 

I  =  length  of  brake  arm  in  feet. 
w  =  net  weight  as  measured  by  the  scale  upon 

which  the  brake  arm  rests. 
n  =  number  of  revolutions  per  minute. 

Indicated  Horsepower. — The  indicated  horsepower  of  an 
internal  combustion  engine  is  measured  in  practically  the  same 


GAS  POWER  PLANT  TESTING  257 

manner  as  in  the  case  of  steam  engines,  but  with  the  following 
differences:  Ordinary  types  of  steam  engine  indicators  are  not 
well  adapted  to  the  testing  of  gas  engines.  The  pressures 
exerted  in  the  gas  engine  cylinder  are  usually  higher  than 
those  common  in  steam  engines  and  are  more  suddenly  applied. 
In  order  to  withstand  these  stresses  the  steam  engine  indicator 
would  have  to  be  equipped  with  a  comparatively  strong  spring. 
The  piston  of  the  gas  engine  indicator  is  usually  made  J"2  the  area 
of  that  of  the  steam  engine  indicator  piston  and  the  springs  are 
interchangeable.  Thus  a  100  pound  steam  indicator  spring 
when  used  with  a  gas  engine  indicator  would  produce  a  one- 
inch  vertical  movement  of  the  pencil  for  a  pressure  of  200  pounds. 

In  calculating  the  indicated  horsepower,  it  must  be  remem- 
bered that  the  complete  cycle  is  not  produced  at  every  revolution 
and  it  is  the  number  of  explosions  rather  than  the  number  of 
revolutions  that  determines  the  horse  power. 

The  formula  for  calculating  the  indicated  horsepower  becomes : 

Lhp-  =  3^000 

In  which 

p  =  mean  effective  pressure  in  pounds  per  square  inch  as  deter- 
mined from  the  indicator  card. 

I  =  length  of  the  engine  stroke  in  feet. 
a  =  area  of  the  piston  in  square  inches. 

e  =  number  of  explosions  per  minute. 

The  Measurement  of  the  Heat  Absorbed  by  the  Jacket  Water. 

The  heat  absorbed  by  the  jacket  water  is  calculated  by  the 
formula : 

W(t2-h) 
In  which 

W  =  the  weight  of  water  passing  through  the  jacket  in  a 

unit  of  time. 
12  =  the  temperature  of  water  discharged  from  the  jacket. 
t\  =  the  temperature  of  the  inlet  water  to  the  jacket. 

The  weight  of  the  jacket  water  is  best  measured  by  the  use  of 
one  or  more  tanks  placed  upon  platform  scales.  During  the 
test  these  tanks  are  alternately  filled,  weighed,  and  emptied. 


258        STEAM  AND  GAS  POWER  ENGINEERING 

Duration  of  Test. — When  the  load  upon  a  gas  or  oil  engine  is 
nearly  constant,  and  can  be  maintained  so  for  an  appreciable 
period,  the  duration  of  the  test  need  not  be  more  than  about  one 
hour.  When  the  load  fluctuates,  longer  periods  are  necessary 
for  accurate  results. 

Starting  the  Test. — Before  starting  a  test  upon  a  gas  or  oil 
engine  sufficient  time  should  be  allowed  for  conditions  to  become 
constant.  The  engine  should  be  operated  at  the  prescribed  load 
until  all  parts  are  thoroughly  heated.  At  a  certain  predeter- 
mined time  the  test  is  started  and  the  regular  measurements  and 
observations  are  made  until  the  test  is  closed. 

Gas  Producer  Testing. — To  ascertain  the  efficiency  of  a  gas 
producer  the  following  data  must  be  obtained:  the  quantity  of 
fuel  used,  the  amount  of  gas  generated,  the  heat  of  combustion  of 
the  fuel,  and  the  heat  of  combustion  of  the  gas. 

The  heat  of  combustion  of  the  fuel  and  of  the  gas  can  be 
determined  by  means  of  the  calorimeters  explained  in  Chapters  II 
and  XII  respectively. 

To  determine  the  amount  of  fuel  used,  the  length  of  the  test 
should  be  such  that  the  total  consumption  of  the  fuel  should  be  at 
least  ten  times  the  weight  of  fuel  contained  in  the  producer  during 
normal  operation.  Producer  tests  of  short  duration  are  inaccu- 
rate.    The  fuel  used  is  weighed  on  platform  scales. 

The  amount  of  gas  generated  is  determined  by  means  of  a 
Venturi  meter,  Pitot  tube,  or  some  other  gas  meter  of  special 
design. 

In  a  complete  test  the  amount  of  power  required  for  driving 
the  fans  and  other  auxiliaries  is  determined,  as  well  as  the  amount 
of  steam  used  and  the  final  purity  of  the  gas. 

A.  S.  M.  E.  Code. — Complete  and  more  detailed  instruction 
concerning  the  testing  of  Gas  Power  Plants  will  be  found  in  the 
Rules  for  Conducting  Performance  Tests  of  Power  Plant  Apparatus, 
published  by  the  American  Society  of  Mechanical  Engineers. 

Problems 

1.  Determine  by  test  the  amount  of  fuel  used  by  an  internal  combustion 
engine  per  brake  horsepower  per  hour. 

2.  Compare  the  heat  consumption  in  B.t.u.  of  the  following  engines  per 
brake  horsepower  per  hour: 


GAS  POWER  PLANT  TESTING  259 

(a)  Gasoline  engine  which  delivers  a  brake  horsepower  per  hour  for  one- 
tenth  of  a  gallon  of  gasoline. 

(b)  Producer  gas  plant  which  consumes  1M  pounds  of  anthracite  coal  per 
B.hp. 

(c)  Diesel  oil  engine  which  consumes  0.47  pounds  of  crude  oil  per  B.hp. 

(d)  Alcohol  engine  which  consumes  one  pound  of  alcohol  per  B.hp. 

3.  Compile  from  the  Power  Test  Code  of  the  American  Society  of  Mechan- 
ical Engineers  a  table  suitable  for  taking  data  in  connection  with  a  complete 
test  on  a  gas  producer  plant. 


CHAPTER  XV 
LOCOMOTIVES 

The  Locomotive  Compared  with  the  Stationary  Steam  Power 
Plant. — On  account  of  requirements  which  must  be  met  in  each 
case,  the  locomotive  and  the  stationary  steam  power  plant  differ 
in  construction.  The  stationary  power  plant  has  practically 
unlimited  space  available.  The  locomotive  is  limited  in  width 
by  the  gage  of  the  track,  and  by  the  clearance  required  for 
station  platforms  and  passing  trains;  it  is  restricted  in  height  by 
the  clearance  of  bridges  and  tunnels;  the  sharpness  of  the  curves 
limit  its  length,  and  its  weight  is  practically  fixed  by  the  strength 
of  bridges  and  by  the  type  of  road  bed.  To  develop  the  variable 
power  demands  to  which  locomotives  are  subjected,  the  boiler 
must  contain  ample  heating  surface  and  at  the  same  time  must 
occupy  small  space.  The  rate  of  combustion  must  be  forced  to 
the  extreme,  as  the  grate  surface  is  limited  in  width  by  the  allow- 
able road  clearance  and  in  length  by  the  distance  a  fireman  can 
spread  the  coal.  In  stationary  plants  10  to  20  pounds  of  coal 
are  ordinarily  burned  per  square  foot  of  grate  surface  when 
operated  with  natural  draft;  in  locomotive  practice,  by  the  use 
of  artificial  draft  150  pounds  or  more  are  usually  burned  per 
square  foot  of  grate  surface. 

Space  limitations  on  locomotives  prohibit  the  use  of  fans  or  of 
high  stacks  for  the  production  of  draft,  and  an  induced  draft 
created  by  the  exhaust  steam  must  be  used.  This  practice 
prevents  the  operation  of  the  engine  condensing  and  makes  diffi- 
cult the  use  of  the  exhaust  steam  in  connection  with  feed  water 
heaters. 

The  Essential  Parts  of  a  Locomotive. — The  essential  parts  of 
a  locomotive  are  illustrated  in  Fig.  203.  The  boiler  (1)  consists  of 
a  cylindrical  shell,  closed  at  its  two  ends  by  tube  plates  which  are 
connected  below  the  water  level  by  numerous  fire- tubes  (3). 

The  furnace,  or  fire-box  (2),  is  an  extension  of  the  boiler  shell, 
the  sides  of  which  extend  downward,  forming  a  chamber  sur- 

260 


LOCOMOTIVES  261 

rounded  at  the  top  and  at  the  bottom  by  water.  The  bottom 
of  the  fire-box  is  fitted  with  a  grate  (24)  upon  which  the  fuel 
is  burned.  Below  the  grate  is  an  ash  pan  (28)  which  retains 
the  ash  until  such  a  time  as  it  may  be  removed.  An  opening 
at  the  back  of  the  fire-box  serves  as  a  fire-door  (23). 

The  furnace  gases  pass  through  the  fire-tubes  and  enter  the 
front-end  or  smoke  box  (4).  In  entering  the  smoke  box,  the 
gases  are  deflected  downward  by  the  diaphragm  or  deflector  plate, 
thence  through  the  spark-arrester  netting  (15),  after  which  they 
mingle  with  the  exhaust  steam  entering  the  smoke  box  from  the 
exhaust  pipe  (11),  and  pass  out  the  stack  (5).  Accumulation  of 
cinders  is  removed  from  the  smoke  box  through  the  spark  chute 
(12),  cleaning  tools  being  inserted  through  the  spark  clean- 
ing hole  (13).  Access  to  the  smoke  box  is  made  through  the  door 
(17),  or  the  entire  smoke  box  cover  (16)  may  be  removed. 

Steam  from  the  boiler  enters  the  steam  dome  (6)  from  which  it 
passes  to  the  engine  cylinder.  The  throttle  lever  (8),  which 
controls  the  valve  in  the  throttle  chamber  (7),  is  used  to  regulate 
the  quantity  of  steam  entering  the  cylinder. 

The  steam  after  passing  through  the  throttle  valve  enters  the 
dry  pipe  (9)  which  passes  through  the  steam  space  and  absorbs  a 
certain  amount  of  heat  from  the  steam  with  which  it  is  in  contact. 
Upon  reaching  the  smoke  box  the  dry  pipe  terminates  in  a  tee 
from  which  two  steam  pipes  (10)  are  used  to  direct  the  steam  into 
the  two  cylinders. 

The  two  cylinders  are  on  the  opposite  sides  of  the  locomotive 
and  the  cranks  are  separated  90  degrees.  Considering  only  one 
cylinder,  the  steam  enters  through  the  valve  (36)  and  after 
performing  its  function  it  passes  through  the  exhaust  pipe  (11) 
and  is  further  utilized  in  creating  the  draft.  When  the  engine 
is  running  the  exhaust  causes  a  constant  movement  of  air  through 
the  furnace  and  tubes . 

The  reversing  of  the  engine,  as  illustrated  in  Fig.  203,  is  accom- 
plished by  the  use  of  the  Walschaert  valve  gear  (see  Chapter  V) . 
The  reversing  lever  (54)  is  located  in  the  engine  cab.  The  reach 
rod  (55)  connects  the  radius  rod  (49),  thus  giving  a  means  for 
controlling  the  position  of  the  link  block  with  respect  to  the  link 
(48)  and  thereby  controlling  the  position  of  the  valves  and  the 
direction  of  the  engine.     The  motion  of  the  link  is  obtained  from 


262       STEAM  AND  GAS  POWER  ENGINEERING 


LOCOMOTIVES  263 


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264       STEAM  AND  GAS  POWER  ENGINEERING 


the  eccentric  crank  arm  (46)  and  the  additional  motion  from  the 
lap  and  lead  lever  (50),  as  shown  in  the  illustration. 

The  injector  (105)  admits  water  to  the  boiler.  Sand  stored 
in  the  box  (91)  is  delivered  to  the  rails  through  the  sand  pipes 
(92)  when  it  is  necessary  to  increase  the  adhesion  of  the  drivers. 
Air  pumps  (83)  deliver  air  to  the  braking  system,  while  such  parts 
as  the  bell  (90),  whistle  (19),  safety  valve  (22),  and  the  head 
light  (86),  need  no  explanation. 

Early  History  of  the  Locomotive. — Locomotives,  if  they  may 
be  designated  by  such  names,  were  built  prior  to  1825,  although 
in  that  year  George  Stephenson  is  credited  with  the  first  locomo- 


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Fig.  204.— The  locomotive  of  1832. 

tive.  Stephenson's  "  Rocket "  was  of  foreign  make,  had  cylinders 
8  in.  by  16%  in.,  weight  about  4  tons,  and  was  capable  of  making 
29  miles  per  hour. 

In  the  United  States  "The  Old  Ironsides,"  built  in  1832  was 
one  of  the  first  locomotives.  As  illustrated  in  Fig.  204,  this  was 
a  four-wheeled  machine;  it  weighed  about  5  tons  and  was  capable 
of  operating  at  a  speed  of  about  30  miles  per  hour. 

The  modern  locomotive  is  a  development  of  the  above  types. 
Its  improvements  paralleled  the  practice  in  steam-power  engi- 
neering. 

Classification  of  the  Locomotive. — Several  methods  for  the 
classification  of  locomotives  are  in  general  use.     One  method 


LOCOMOTIVES 


265 


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266        STEAM  AND  GAS  POWER  ENGINEERING 

quite  commonly  used  is  based  upon  the  wheel  arrangement. 
This  system  indicates  the  number  of  truck,  driving,  and  trailer 
wheels.  Thus  a  262  type  would  signify  a  machine  having  a 
two-wheeled  front  truck,  6  drivers,  and  a  two-wheeled  trailing 
truck.  Table  8  gives  the  wheel  arrangement,  the  designating 
name,  and  the  numerical  symbol  of  the  various  types  of  locomo- 
tives. 

The  Development  of  the  Locomotive. — The  development  of 
the  locomotive  to  its  present  state  has  resulted  from  the  demands 
for  machines  of  larger  haulage  capacity.  The  greatest  difficulty 
found  was  in  securing  the  larger  boiler  and  grate  areas  which  were 
necessary.  The  method  by  which  these  features  were  met  is 
best  illustrated  by  considering  those  types  of  locomotives  which 
were  especially  designed  for  passenger  traffic. 

The  American  type,  or  the  eight  wheel,  440,  was  once  con- 
sidered the  standard  locomotive  for  passenger  service,  while  at 
the  present  time  its  use  is  confined  to  light  service. 

The  Atlantic  type,  442,  was  developed  from  the  American 
type,  and  in  general  the  difference  between  the  two  types  is  the 
addition  of  a  trailing  truck.  By  this  design  the  boiler-heating 
surface  could  be  enlarged,  while  the  use  of  the  trailing  truck 
rather  than  another  set  of  drivers  made  space  for  the  necessary 
additional  fire-box  capacity. 

The  Pacific  type,  462,  is  the  development  of  the  Atlantic 
type  using  the  same  general  design.  The  insertion  of  an  addi- 
tional driver  is  to  distribute  the  weight  by  not  having  it  concen- 
trated upon  two  drivers,  thereby  increasing  the  rail  contact  and 
the  amount  of  adhesion. 

The  Mallet  Articulated  Compound. — The  need  for  larger 
powered  locomotives  and  trie  limiting  conditions  to  which  the 
locomotive  in  its  construction  is  subjected  leaves  practically  but 
one  course  to  follow  if  any  increase  in  capacity  is  to  be  made  and 
that  is  by  increasing  the  number  of  drivers  or  the  length  of  the 
engine.  To  increase  the  length  and  maintain  a  rigid  type  was  out 
of  the  question  on  account  of  the  difficulties  and  dangers  in 
rounding  curves. 

The  articulated  compound  locomotive,  illustrated  in  Fig.  205, 
has  been  designed  to  meet  the  above  conditions.  This  type 
consists  of  two  sets  of  engines  under  one  boiler.     The  rear  set 


LOCOMOTIVES 


267 


is  fixed  rigidly  to  the  boiler  while  the  front  set  supports  the 
overhanging  end  of  the  boiler  and  is  capable  of  adjusting  itself 
to  the  alignment  of  the  road.  The  two  sets  of  engines  are  hinged 
together  and  exhaust  pipes  from  one  set  of  cylinders  to  the  other 
are  made  flexible  by  ball  and  socket  joints.  The  steam  from  the 
boiler  enters  the  high  pressure  cylinders  and  exhausts  into  the 
low  pressure  cylinders,  which  are  located  on  the  front  engine,  from 
which  the  steam  exhausts  as  is  the  case  in  other  types. 

The  most  powerful  locomotives  are  of  the  articulated  type. 
While  little  used  at  the  present  time  in  passenger  service,  they 
have  been  very  satisfactory  in  heavy  freight  service  especially 
on  roads  having  heavy  gradients  combined  with  sharp  curves. 


Fig.  205. — Articulated  compound  locomotive. 

Locomotive  Superheaters. — Two  types  of  superheaters  are 
used  in  locomotive  practice:  one  receives  its  heat  wholly  from 
the  gases  in  the  smoke  box,  the  other  receives  part  of  its  heat  from 
the  smoke  box,  but  the  greater  amount  of  heat  is  derived  from 
superheater  elements  extending  into  the  tubes. 

The  smoke  box  type  is  constructed  wholly  within  the  smoke 
box,  requiring  little  or  no  change  in  the  usual  boiler  arrangement, 
but  has  the  disadvantage  of  being  limited  to  low  degrees  of  super- 
heat. It  consists  of  two  small  cast  steel  drums  connected  to 
each  of  the  steam  pipes,  while  numerous  small  tubes  complete 
the  path  of  the  steam.  The  steam  entering  the  upper  drum 
passes  through  the  tubes  and  absorbs  heat  from  the  flue  gases 
which  surround  them. 

One  type  of  locomotive  superheater  is  illustrated  in  Fig.  206. 
As  usually  constructed  this  superheater  consists  of  a  box  or 
header  A  located  in  the  smoke  box  to  which  are  attached 
numerous    superheating    elements.     These    elements    are    con- 


268       STEAM  AND  GAS  POWER  ENGINEERING 

structed  of  seamless  steel  tubing  and  return  bends,  and  are 
located  in  large  fire-tubes  C  through  which  the  furnace  gases 
pass.  The  steam  is  thus  made  to  pass  through  a  superheating 
element  before  entering  the  cylinder.  The  flow  of  gases  over 
the  superheater  surface  is  controlled  by  a  damper  D  which  is 
operated  by  the  cylinder  E.  When  the  engine  throttle  is  closed 
the  damper  is  similarly  closed,  thus  protecting  the  superheater 
tube.  When  the  throttle  is  opened  and  steam  is  passing  through 
the  superheater,  the  damper  is  automatically  opened. 


Fig.  206. — Locomotive  superheater. 

Locomotive  Stokers. — Many  different  designs  of  stokers  have 
been  applied  to  locomotives.  The  chief  advantage  in  the  use  of  a 
mechanical  stoker  lies  in  the  facility  for  the  burning  of  a  greater 
amount  of  coal  and  in  the  possibility  of  using  cheaper  fuels  than 
is  possible  with  hand  firing. 

Fig.  207  illustrates  one  type  of  locomotive  stoker  suitable  for 
nut  and  slack  coal.  It  consists  of  a  screw  conveyor  placed  under 
the  floor  of  the  tender  and  three  distributing  nozzles  for  spraying 
the  coal  over  the  fire. 

Coal  from  the  tender  passes  first  through  regulating  screens, 
thence  by  a  screw  conveyor  to  the  engine  cab,  and  is  finally  deliv- 


LOCOMOTIVES 


269 


ered  to  the  distributing  nozzles  from  which  it  is  fed  to  the  furnace 
by  means  of  a  steam  blast.  Of  the  three  distributing  nozzles 
shown  the  central  one  utilizes  the  fine  coal  and  feeds  the  center 
of  the  furnace.  The  remaining  two  are  supplied  with  coarser 
coal  and  feed  the  two  sides  of  the  furnace. 


Fig.  207. — Locomotive  stoker. 


Draft  Appliances. — A  typical  front-end  is  illustrated  in  Fig. 
208.  The  exhaust  steam  from  the  cylinders  passes  through  the 
exhaust  ports  into  the  exhaust  pipe  E,  which  terminates  in  a 
restricted  area  or  exhaust  tip.  This  arrangement  regulates  the 
velocity  of  the  exhaust  and  the  intensity  of  the  draft.  A  small 
opening  creates  an  intense  draft,  but  at  the  same  time  raises  the 
back  pressure  in  the  cylinder.     The  nozzle  is  arranged  so  that 


270        STEAM  AND  GAS  POWER  ENGINEERING 

sufficient  draft  is  obtained  and  the  back  pressure  in  the  cylinders 
is  as  low  as  possible. 

The  stack  extension  or  "  Petticoat  Pipe/'  P,  is  used  when  the 
exhaust  nozzle  is  low.  This  is  used  as  an  additional  channel  to 
conduct  the  steam  which,  if  not  used,  would  fill  the  smoke-box, 
thus  destroying  the  draft.  The  diaphragm  D  begins  above  the 
top  row  of  tubes  and  terminates  in  a  movable  slide  S,  which  may 
be  raised  or  lowered  to  meet  varying  conditions.  The  diaphragm 
acts  first  to  deflect  the  solid  particles  in  the  gases  downward  and 
second  as  a  draft  regulating  device.  Without  the  diaphragm 
the  upper  rows  of  tubes  would  be  greatly  affected  by  the  exhaust. 
This  would  produce  uneven  burning  of  the  fuel  over  the  surface 


\ 

^                   J     \ 

i 

^  f = 

1  r     " 

3i 

4 

Fig.  208. — Locomotive  front  end. 


of  the  grate.  By  regulating  the  diaphragm  the  draft  can  be 
made  uniform  over  the  entire  grate  surface. 

Injectors. — The  injector  as  a  means  of  introducing  feed  water 
into  a  boiler  is  seldom  used  in  stationary  power  plant  practice. 
It  is  the  general  impression  that  the  injector  is  not  as  reliable  as 
the  reciprocating  pump  and  in  addition  cannot  pump  hot  water. 
Its  chief  advantage  is  due  to  the  small  space  it  occupies  and  this  fact 
makes  it  practical  for  use  on  locomotives,  where  space  economy 
is  important.  To  overcome  the  possibilities  of  failure  to  operate, 
locomotives  are  equipped  with  two  injectors.  If  one  injector 
becomes  inoperative  the  other  may  be  relied  upon. 

Air  Brakes. — One  of  the  first  types  of  air  braking  systems  was 
what  was  generally  known  as  the  Straight  Air  Brake.  This  con- 
sisted of  a  steam  driven  air  pump  located  on  the  engine,  a  reservoir 


LOCOMOTIVES 


271 


272       STEAM  AND  GAS  POWER  ENGINEERING 

in  which  compressed  air  was  stored,  a  pipe  line  extending  through- 
out the  length  of  the  train,  each  car  being  connected  by  flexible 
hose  couplings,  and  a  brake  cylinder  on  each  car  the  piston  of 
which  was  directly  connected  to  the  brake  levers.  The  engineer's 
valve  could  admit  air  to  the  piping  and^thence  to  the  cylinder 
causing  the  brakes  to  act,  or  could  discharge  the  air  from  the 
braking  system  or  train  line,  thus  releasing  the  brakes. 

Experience  demonstrated  that  the  use  of  the  straight  air  brake 
system  is  dangerous  when  used  on  trains.  The  hose  connection 
between  cars  often  broke  resulting  in  the  loss  of  the  braking  effect 
throughout  the  entire  train.  When  the  train  would  brake  apart 
the  rear  part  often  overtook  that  of  the  front  with  the  possibility 
of  a  serious  collision  and  damage.  It  was  found  necessary  to 
have  an  automatic  system  and  this  led  to  the  introduction  of 
the  indirect  or  automatic  system  which  is  still  used. 

The  automatic  system  operates  by  decreasing  the  air  pressure 
in  the  train  line  rather  than  by  increasing  it  as  in  the  case  of  the 
direct  air  system.  A  diagrammatic  layout  of  an  automatic  system 
is  illustrated  in  Fig.  209.  A  compressor  delivers  air  to  a  main 
reservoir  which  is  connected  through  the  engineers  valve  to  the 
train  line.  Under  each  car  is  another  reservoir,  termed  the 
auxiliary  reservoir,  a  brake  cylinder  and  triple  valve  controlling 
air  to  and  from  the  brake  cylinder. 

When  the  engine  is  coupled  to  the  train,  air  is  admitted  to  the 
train  line,  passes  through  the  triple  valve,  and  enters  the  auxil- 
iary reservoir.  When  air  is  released  from  the  train  line,  the 
lowering  in  pressure  causes  the  triple  valve  to  operate  permitting 
the  air  in  the  auxiliary  reservior  to  be  transferred  to  the  brake 
cylinder,  thus  the  brakes  are  applied.  In  this  system  if  a  coup- 
ling hose  should  burst  or  the  train  part,  the  brakes  would  be  set 
because  of  the  lowering  of  the  pressure  in  the  train  line. 

Problems 

1.  In  which  respects  does  the  locomotive  power  plant  differ  from  the 
ordinary  stationary  steam  power  plant? 

2.  Ascertain  what  reversing  mechanism  is  used  on  the  locomotives  passing 
through  your  city. 

3.  Compare  the  air-brake  system  used  on  electric  street  cars  in  your  city 
with  the  automatic  air  brakes  as  used  on  locomotives. 


CHAPTER  XVI 
AUTOMOBILES,   TRUCKS  AND  TRACTORS 

Automobiles 

Types  of  Automobiles. — Automobiles  are  propelled  by  internal 
combustion  engines,  by  steam  engines,  or  by  electric  motors  with 
current  secured  from  storage  batteries. 

At  the  present  time  a  very  large  majority  of  automobiles  are 
driven  by  internal  combustion  engines  using  gasoline  as  fuel. 
The  gasoline  automobiles  possess  the  following  advantages :  they 
are  manufactured  in  many  different  types  and  designs,  can  be 
secured  at  a  wide  range  of  prices,  are  more  economical  than  other 
types,  and  are  usually  provided  with  a  fuel  storage  of  sufficient 
capacity  to  propel  the  car  several  hundred  miles.  The  disadvan- 
tages of  the  gasoline  automobile  are  that  it  is  not  self -starting, 
lacks  over-load  capacity,  and  must  be  built  with  a  complicated 
system  of  gears  for  speed  changing  and  for  reversing. 

The  automobile  propelled  by  a  steam  engine  is  very  flexible, 
is  easily  controlled,  and  has  a  very  large  range  of  power.  To  off- 
set these  advantages,  the  steam  automobile  requires  considerable 
time  to  start  after  a  long  stop,  as  steam  must  be  generated  in  the 
automobile  boiler  before  the  engine  will  start.  This  fault  is 
being  greatly  remedied  in  some  of  the  recent  steam  automobiles, 
but  all  steam  automobiles  require  considerable  skill  in  opera- 
tion, as  constant  attention  must  be  given  to  the  fuel  and  water 
supply. 

The  electric  automobile  is  also  very  flexible,  operates  more 
quietly  than  other  types,  is  clean,  and  is  easy  to  start  and  to  con- 
trol. The  greatest  disadvantage  of  the  electric  car  is  that  it 
can  run  only  for  short  distances  without  recharging  its  storage 
batteries.  The  use  of  the  electric  automobile  is  limited  mainly 
to  cities  where  facilities  are  available  for  charging  storage  bat- 
teries.    Electric  cars  are  also  expensive  to  operate. 

As  steam  and  electric  automobiles  are  not  generally  used,  this 
chapter  will  deal  only  with  the  gasoline  automobile, 
is  273 


274        STEAM  AND  GAS  POWER  ENGINEERING 

Essential  Parts  of  a  Gasoline  Automobile. — The  essential  parts 
of  a  gasoline  automobile  are : 

1.  A  power  plant,  which  consists  of  an  internal  combustion 
engine  and  its  auxiliaries,  such  as  the  fuel  system,  carburetor, 
ignition  system,  and  cooling  and  lubricating  systems.  In  some 
cars  this  also  includes  the  starting  equipment. 

2.  Friction  clutch,  for  disengaging  the  engine  from  the  pro- 
pelling mechanism. 

3.  Transmission  mechanism  for  speed  changing  and  reversing. 

4.  Differential  gear,  the  purpose  of  which  is  to  allow  one  drive 
wheel  to  revolve  independently  of  the  other,  this  being  necessary 
when  turning  corners. 

5.  Front  and  rear  axles. 

6.  The  frame  for  supporting  the  power  plant,  the  transmission 
system,  and  the  body  of  the  car.  Interposed  between  the  body 
and  the  axles  are  the  springs,  which  are  built  up  from  a  number  of 
leaves. 

7.  Control  system,  which  includes  the  steering  mechanism, 
hand  levers  and  foot-pedals,  means  for  controlling  the  spark 
position,  the  carburetor  throttle,  the  clutch,  the  transmission 
gearing,  and  the  brakes. 

8.  Wheels,  tires,  lights,  alarm,  body,  top,  fenders,  dash,  run- 
ning board,  wind  shield,  and  speedometer. 

The  term  chassis  is  applied  to  the  car  with  the  body  and  acces- 
sories removed. 

Automobile  Motors. — Modern  automobiles  use  four,  six,  eight, 
or  twelve-cylinder  motors.  The  motors  are  all  of  the  vertical 
type  and  operate  on  the  Otto  four-stroke  cycle.  The  engine  is 
mounted  in  the  front  end  of  the  car  for  accessibility,  and  also 
for  the  purpose  of  more  evenly  distributing  the  weight  of  the  car. 
Multi-cylinder  motors  permit  of  easier  starting,  operate  more 
smoothly,  run  with  less  vibration,  and  have  a  wider  range  of 
power.  Four  and  six-cylinder  engines  have  all  cylinders  in  one 
row  and  located  on  one  side  of  the  crankshaft.  Eight-cylinder 
engines  have  their  cylinders  V-type  in  two  rows  with  the  rows 
set  at  an  angle  of  90  degrees.  Twelve-cylinder  engines  are  of  the 
V-type  and  have  two  rows  of  cylinders  set  at  an  angle  of  60 
degrees. 

The  cylinders  may  be  cast  singly  or  en-bloc;  the  en-bloc  con- 


AUTOMOBILES,  TRUCKS  AND  TRACTORS       275 

struction  means  that  several  cylinders  are  cast  in  one  piece.  The 
single-cylinder  casting  is  light  in  weight  and  is  easily  replaced. 
The  en-bloc  motor  is  more  rigid,  occupies  less  space  and  is  the 
more  commonly  used. 

Cooling  of  Automobile  Motors. — Automobile  motors  are  gener- 
ally water-cooled  and  are  provided  with  radiators  for  the  purpose 
of  cooling  the  water  after  it  has  absorbed  heat  from  the  cylinder 
walls.  Either  the  thermosyphon  or  the  forced  water  circulation 
system  is  used. 


Fig.  210. — Thermo-syphon  water-circulation  system. 

The  thermo-syphon  system  (Fig.  210)  depends  upon  the  fact 
that  water  rises  when  heated.  This  system  does  not  require  a 
pump  to  circulate  the  water.  The  water  enters  the  cylinder 
jackets  at  A  (Fig.  210).  Upon  becoming  heated  by  the  explo- 
sions going  on  within  the  cylinder  of  the  engine,  the  water  rises 
to  the  tops  of  the  cylinder  jackets,  entering  the  pipe  B  and  passing 
into  the  radiator  at  C  where  it  is  brought  into  contact  with  the 
radiator  cooling  surfaces.  On  being  cooled,  the  water  becomes 
heavier  and  sinks  to  the  bottom  of  the  cooling  system,  to  enter 
the  cylinder  once  more  and  to  repeat  its  circulation.  The  cooling 
action  of  the  radiator  is  increased  by  the  fan  F  which  draws  air 
through  the  radiator  spaces. 


276        STEAM  AND  GAS  POWER  ENGINEERING 

The  forced  circulation  cooling  system  differs  from  the  thermo- 
syphon  system  in  that  it  has  a  circulating  pump  to  aid  in  the 
circulation.  The  pump  which  is  usually  of  the  centrifugal  type 
makes  the  circulation  more  positive.  The  course  taken  by  the 
circulating  water  is  exactly  the  same  in  both  systems. 

Some  air-cooled  automobile  motors  have  proven  very  satis- 
factory. The  cylinders  of  air-cooled  motors  are  ribbed  to  increase 
the  radiating  surface  and  the  circulation  of  the  air  is  produced  by 
means  of  a  fan  located  in  the  motor  fly  wheel. 

Lubrication. — Five  methods  are  used  for  lubricating  automobile 
motors : 

1.  The  splash  system.  This  system  depends  entirely  upon 
dippers  on  the  connecting  rods  to  splash  the  oil  to  the  various 
parts  of  the  motor. 


Fig.  211. — Motor  with  poppet  valves. 


2.  The  circulating  splash  system.  This  differs  from  the 
straight  splash  method  in  that  a  pump  at  a  low  point  in  the  crank 
case  delivers  the  oil  to  troughs  under  the  connecting  rods.  From 
these  troughs  the  dippers  splash  the  oil  in  the  same  manner  as 
in  the  straight  splash  system. 

3.  The  forced  splash  system.  This  system  uses  a  pump  to  force 
the  oil  to  the  main  bearings  and  to  the  troughs  previously  men- 
tioned. Dippers  on  the  connecting  rods  then  splash  the  oil  in 
the  same  manner  as  mentioned  before.  This  system  differs  from 
the  circulating  splash  in  that  the  oil  is  forced  to  the  main  bearings. 

4.  The  forced  system.  This  system  has  a  hollow  or  drilled 
crankshaft  through  which  the  oil  is  forced  from  the  main  bearings 


AUTOMOBILES,  TRUCKS  AND  TRACTORS       277 

to  the  connecting-rod  bearings  and  is  then  splashed  to  the  wrist 
pin  and  cylinder  walls. 

5.  The  full  forced  system.     This  system  has  tubes  leading  up 
along  the  connecting  rods  to  the  wrist  pin.     The  oil  is  forced 


1.  Cylinder. 

2.  Water-jacketed    cylinder 

head. 

3.  Spark  plug. 

4.  Inner  sleeve. 

5.  Outer  sleeve. 

6-7.  Port  openings  in  sleeves. 

8.  Priming  cup. 

9.  Oiling  grooves  in  sleeves. 

10.  Port  opening  in  cylinder. 

11.  Connecting-rod  operating 

outer  sleeve. 

12.  Connecting-rod  operating 

inner  sleeve. 


13.  Fly  wheel. 

14.  Oil  trough  adjusting  lever 

connected  to  throttle. 

15.  Lower  part  of  crank  case, 

containing      oil      pump, 
strainer  and  piping. 

16.  Oil  scoop. 

17.  Adjustable  oil  troughs. 

18.  Crank  shaft. 

19.  Crank-shaft  bearing. 

20.  Starting  clutch. 

21.  Silent     chain     drive     for 
magneto  shaft. 


22.  Silent  chain  driving  sprock- 

et for  electric  generator 
(on  4-cylinder  models). 

23.  Silent     chain      drive     for 

eccentric  shaft. 

24.  Eccentric  shaft. 

25.  Connecting  rod. 

26.  Bearing  for  eccentric  shaft. 

27.  Piston. 

28.  Piston  rings. 

29.  Cylinder- head  ring    (junk 

ring) . 


Fia.  212. — Sectional  view  of  Sterns-Knight  four-cylinder  motor. 

by  the  pump  to  the  main  bearings,  thence  through  the  crank-shaft 
to  the  connecting-rod  bearings,  thence  through  the  tubes  to  the 
wrist  pin,  and  through  the  hollow  wrist  pin  to  the  cylinder  walls. 
With  a  full-forced  system  a  relief  valve  is  provided  to  prevent  the 
oil  pressure  from  becoming  excessive. 


278        STEAM  AND  GAS  POWER  ENGINEERING 


The  parts  of  the  automobile  motor  which  require  lubrication 
are  the  main  shaft  bearings,  crank-pin  bearings,  wrist-pin  bear- 
ings, cam  shaft  bearings,  timing  gears,  cams,  cam  lifter  guides, 
cylinder  walls,  and  other  moving  parts,  such  as  yokes  and  ends 
of  rods. 

Automobile  Valves. — The  poppet  type  of  valve,  Fig.  211,  is 
generally  used  on  automobile  motors.  The  sleeve  valve  type  of 
motor  (Fig.  212)  is  also  used  on  certain  designs  of  automobiles. 

Poppet  valve  motors  are  built  in  several  forms  according  to 
location  of  valves. 


Fig.  213. — Ell-head  cylinder.    Fig.  214. 


-Tee-head  cylinder.  Fig.  215. — Valves-in-the 
head  cylinder. 


1.  The  ell-head  motor  (Fig.  213)  has  both  the  intake  and 
exhaust  valves  on  one  side  of  the  cylinder. 

2.  The  tee-head  motor  (Fig.  214)  has  the  exhaust  valves  on 
one  side  of  the  cylinder  and  the  intake  valves  on  the  other. 

3.  The  valve-in-the-head  or  I-head  motor  (Fig.  215)  has 
both  intake  and  exhaust  valves  in  the  cylinder  head. 

4.  The  combination  ell-head  and  valve-in-head,  sometimes 
known  asF-head,  has  the  intake  valve  in  the  head  and  the  exhaust 
valve  on  the  side  of  the  head. 


AUTOMOBILES,  TRUCKS  AND  TRACTORS       279 

Clutches. — The  clutch  is  a  device  used  for  connecting  the 
engine  to,  and  disconnecting  it  from,  the  propelling  gear  of  the 
car.  Clutches  depend  upon  the  frictional  adhesion  between 
surfaces  and  are  of  two  general  types. 

1.  The  cone  clutch,  illustrated  in  Fig.  216,  consists  of  a  leather- 
faced  cone  C  which  is  pressed  by  the  spring  S  against  the  inside  of 
the  tapered  rim  of  a  fly  wheel  W. 


Fig.  216. — Cone  clutch. 

2.  The  multiple  disk  clutch  (Fig.  217)  depends  for  its  action 
upon  the  friction  between  disks.  Alternate  disks  are  fastened 
to  the  driving  and  driven  parts.  The  disks  marked  A  are  fas- 
tened to  the  engine  shaft  and  those  marked  B  connect  with  the 
mechanism  to  be  driven.  If  the  clutch  runs  in  a  bath  of  oil  it  is 
called  a  wet-disk  clutch.  A  spring  is  employed  to  hold  the  disks 
in  contact  when  the  clutch  is  in  action. 


280        STEAM  AND  GAS  POWER  ENGINEERING 

Transmissions. — The  speed  of  an  internal  combustion  engine 
and  its  direction  of  rotation  cannot  be  varied  to  meet  the  re- 
quirements of  an  automobile.  This  necessitates  the  introduction 
of  some  form  of  mechanism  for  speed  changing  and  also  for  re- 
versing, in  order  that  different  speed  ratios  and  reversal  of  direc- 
tion can  be  secured  between  the  engine  and  the  drive  axle.  The 
mechanism,  which  is  used  in  speed  changing  and  in  reversing, 
is  known  as  the  transmission.  The  transmission  is  so  constructed 
that  the  propelling  ability  of  the  motor  is  increased  at  the  expense 


Fig.  217. — Multiple-disk  clutch. 


of  the  speed  of  the  automobile.  That  is,  the  motor  through  the 
gear  ratios  of  the  transmission  is  able  to  pull  a  larger  load  at  a 
lower  speed  than  it  could  by  direct  drive. 

Only  two  types  of  transmissions  are  now  extensively  used,  the 
selective  sliding  and  the  planetary  type.  The  progressive  sliding 
type  and  the  friction  drive  are  practially  out  of  date. 

Fig.  218  illustrates  the  selective  sliding  gear  transmission 
system.     The  desired  gear  ratio  can  be  obtained  by  means  of 


AUTOMOBILES,  TRUCKS  AND  TRACTORS       281 

this  type  of  transmission  without  shifting  through  other  posi- 
tions.    This  system  is  most  generally  used. 

In  Fig.  218,  A  is  the  driving  shaft,  B  the  driven  shaft.  $  and 
L  are  slides  carrying  yokes  that  move  on  the  wheels  D  and  K. 
All  the  wheels  on  the  counter  shaft  are  fast  to  the  shaft.  A  lever 
is  arranged  for  shifting  either  S  or  L  and  for  allowing  the  various 
gears  on  the  shaft  B  to  mesh  with  those  on  the  counter  shaft. 
This  system  is  usually  arranged  for  three  speeds  forward  and  one 
speed  reverse,  but  can  be  modified  for  any  number  of  speeds  for- 
ward and  for  reversing.  For  reversing  an  idler  gear  is  provided 
between  the  driver  and  driven  gears.     High  speed  forward  is 


XZt <zs 

Fig.  218. — The  selective  sliding-gear  transmission  system. 

usually  direct  drive.     Some  cars  have  transmissions  which  per- 
mit of  a  higher  speed  than  the  direct  drive. 

In  the  planetary  transmission  system,  speed  changes  do  not 
depend  upon  the  shifting  of  gears,  but  clutches  or  brakes  are 
applied  to  hold  certain  wheels  in  position.  The  drive  is  positive 
and  the  gears  are  always  in  mesh.  For  high  speeds  this  system 
is  very  well  adapted,  as  the  entire  system  is  clamped  solidly  and 
revolves  with  the  motor  crank  shaft  as  a  single  mass.  As  no 
gears  are  turning  idly  the  entire  system  by  its  weight  serves  to 
steady  the  rotation  of  the  motor  at  high  speeds.  The  planetary 
system  provides  only  two  speeds  forward  and  one  reverse.  It  is 
inefficient  in  low  speed  and  reverse,  as  much  power  is  absorbed 


282       STEAM  AND  GAS  POWER  ENGINEERING 

by  friction  in  the  gears  and  clutches.     The  use  of  the  planetary 
system  is  limited  to  small  automobiles. 

Differentials  for  Automobiles.— Differential  gears,  sometimes 
called  compensating  gears,  are  provided  to  permit  one  wheel 


Fig.  219. — Bevel-gear  differential. 


to  turn  faster  than  the  other  on  turning  corners  or  when  meeting 
obstructions.  The  outside  wheel  in  turning  a  corner  has  the 
greater  distance  to  travel  than  has  the  inside  wheel  in  the  same 
length  of  time.  In  automobiles  the  differential  is  a  part  of  the 
rear  axle  assembly.     If  two  drive  wheels  were  rigidly  connected 


AUTOMOBILES,  TRUCKS  AND  TRACTORS       283 

without  a  differential  it  would  be  necessary  for  one  wheel  to 
skid  or  slip  when  turning  a  corner  or  when  going  over  an  obstruc- 
tion, thereby  throwing  great  strain  on  the  parts  and  producing 
excessive  wear  on  the  tires. 

The  bevel  gear  differential  (Fig.  219)  is  usually  used  on  auto- 
mobiles. The  rear  axle  S  (Fig.  219)  is  divided  into  two  halves. 
Each  half  of  the  rear  axle  carries  a  drive  wheel  at  its  outer  end 
and  a  bevel  gear  (C  or  Z>)  at  its  inner  end.  The  bevel  gears  C 
and  D  are  connected  by,  from  two  to  four,  differential  or  compen- 
sating pinions  (B,  B,  B)  which  are  placed  at  equal  distances  apart 
around  the  circle.  These  bevel  pinions  (B,  B,  B)  are  capable  of 
rotating  loosely  on  radial  studs,  which  are  fastened  at  their  outer 
ends  to  the  casing  or  housing  0.  The  gear  A  is  made  to  turn 
loosely  upon  the  hubs  of  the  bevel  gear  C  and  D,  but  is  made  fast 
to  the  housing  0  by  means  of  bolts  or  rivets.  The  power  from  the 
engine  is  transmitted  to  the  housing  0  through  the  bevel  gear 
pinion  P  which  meshes  with  gear  A.  The  housing  transmits  this 
power  through  the  small  bevel  pinions  (B,  B,  B)  to  the  bevel  gears 
C  and  Z>,  which  are  connected  to  the  rear  or  drive  wheels.  On  a 
level  road  with  both  drive  wheels  rotating  at  the  same  speed,  the 
housing  0,  with  all  the  gears  and  pinions  will  revolve  as  one  mass, 
and  the  small  pinions  (B,  B,  B)  will  remain  stationary.  The  wheel 
which  turns  the  more  easily  is  always  the  one  to  turn.  In  turning 
a  corner,  in  meeting  an  obstruction,  in  case  one  of  the  wheels 
slips,  or  if  the  drive  wheel  attached  to  the  bevel  gear  C  must  turn 
slower  than  that  attached  to  gear  D,  the  differential  pinions  (B,  B, 
B)  will  revolve  on  their  axes.  The  bevel  pinions  (B,  B,  B)  divide 
the  torque  between  the  two  bevel  gears  C,  D,  thereby  permitting 
the  two  drive  wheels  to  run  at  different  speeds. 

Universal  Joint. — Since  the  engine  and  the  gearing  are  mounted 
on  the  frame  of  the  automobile,  while  the  driving  wheels  are 
connected  to  the  frame  by  springs,  automobiles  must  be  provided 
with  one  or  more  flexible  joints.  The  flexible  joint  is  known  as  a 
universal  joint  and  consists  of  two  forked  arms  at  the  ends  of 
shafts.  These  forked  arms  are  joined  by  pins  through  their  ends 
to  a  center  member  and  are  arranged  so  that  the  pin  of  one  forked 
arm  lies  in  the  same  plane,  but  at  right  angles  to  the  pin  of  the 
other.  This  permits  the  lower  end  of  the  propeller  shaft  to  move 
independently  of  the  motion  of  the  rear  axle. 


284        STEAM  AND  GAS  POWER  ENGINEERING 

Front  and  Rear  Axles. — The  front  axles  are  of  a  construction 
which  permits  the  wheels  to  pivot  near  the  hub.  This  reduces 
the  tendency  of  the  wheel  to  swing  when  striking  an  obstruction 
in  the  road.  The  steering  knuckles  are  the  part  of  the  front  axle 
assembly  on  which  the  wheels  revolve.  Steering  arms  are  inserted 
in  the  knuckles  and  are  connected  together  with  an  adjustable 
tie  rod  so  that  both  knuckles  turn  simultaneously.  A  third  arm, 
usually  on  the  left  hand  knuckle,  is  connected  to  the  steering 
gear  by  means  of  the  steering  connecting  rod.  Automobile 
front  axles  are  drop  forged  with  I-beam  cross  sections. 

Rear  axles  for  automobiles  are  live  axles;  that  is,  they  turn  with 
the  wheels.  They  are  divided  into  3  types :  the  semi-floating,  the 
three-quarter  floating,  and  the  full-floating.  In  the  semi-floating 
type  the  entire  load  is  carried  on  the  axle.  The  bearing  in  a  three- 
quarter  floating  is  on  the  housing  and  the  wheel  is  keyed  to  the 
axle;  with  this  type  it  is  not  possible  to  remove  the  axle  without 
also  removing  the  wheel.  When  a  full-floating  axle  is  used  the 
bearing  is  also  on  the  axle  housing  and  the  entire  weight  is  sup- 
ported on  the  housing.  With  the  full-floating  type  of  rear  axle 
the  only  strain  on  the  axle  is  the  torque  in  turning  the  wheel ;  as 
the  axle  is  not  fastened  rigidly  at  either  end  it  can  be  taken  out 
without  disturbing  the  wheel,  by  removing  the  hub  flange. 

Steering  and  Control  Systems. — Automobiles  are  steered  by 
means  of  a  hand  wheel  which  is  located  on  top  of  the  steering 
column.  The  steering  gear  operates  on  the  front  axle,  through 
the  steering  connecting  rod,  and  turns  the  knuckles  and  the 
front  wheels.  The  steering  column,  besides  the  steering  mechan- 
ism, usually  contains  several  concentric  tubes  with  connections  to 
the  alarm,  the  throttle  control,  and  the  spark  control. 

The  spark  and  the  carburetor  throttle  control  levers  are 
usually  located  on  top  of  the  steering  wheel.  On  some  cars  they 
are  located  below  the  steering  wheel. 

Most  modern  cars  are  provided  with  two  methods  of  throttle 
control,  the  hand  throttle  control  on  the  steering  column  and  a 
foot  control,  known  as  the  accelerator. 

The  foot  accelerator  and  the  hand  throttle  control  are  so  con- 
nected that  the  hand  accelerator  also  works  the  foot  accelerator, 
but  the  operation  of  the  foot  accelerator  does  not  change  the 
position  of  the  hand  control. 


AUTOMOBILES,  TRUCKS  AND  TRACTORS       285 

The  control  system  includes  a  pedal  for  operating  the  friction 
clutch,  one  for  operating  the  service  brake,  a  lever  for  operating 
the  emergency  brake,  and  a  lever  for  operating  the  speed  changing 
and  reversing  gears  of  the  transmission.  In  some  makes  of  cars 
the  service  brake  is  operated  by  the  clutch  pedal  and  the  emer- 
gency by  the  other  foot  pedal. 

The  Ford  automobile  is  controlled  by  three  foot  pedals  and  by 
one  hand  lever.  The  pedals  operate  the  clutch,  the  reverse,  and 
the  service  brake.  The  hand  lever  operates  the  clutch  and  the 
emergency  brake. 

Brakes. — Automobile  tires  being  made  of  rubber,  the  brakes 
are  not  applied  to  the  wheel  tires,  but  to  metal  drums  which  are 
fastened  to  the  rear  wheels.  Two  brakes  are  employed.  One 
brake  called  the  service  brake,  is  operated  by  means  of  a  foot  pedal. 
The  other  brake,  called  the  emergency  brake,  is  usually  operated 
by  a  hand  lever  and  is  intended  for  use  only  in  case  the  service 
brake  fails  or  in  case  a  very  strong  braking  action  is  required. 
The  braking  effect  can  be  produced  by  expanding  the  brake  band 
or  shoe  within  the  brake  drum  or  by  contracting  the  brake  shoe 
around  the  outside  of  the  brake  drum.  Automobiles  usually 
have  an  external  contracting  brake  for  service,  and  an  internal 
expanding  brake  for  the  emergency  brake. 

The  brake  bands  are  usually  covered  on  the  rubbing  side  with 
an  asbestos  preparation,  which  can  be  replaced  when  worn  out. 

Wheels  and  Tires. — Automobile  wheels  may  be  made  of  wood 
or  of  metal.  On  most  cars  the  wooden  wheels  go  with  the  stand- 
ard equipment.  Wire  wheels  are  light  in  weight,  but  require  care 
to  keep  all  the  spokes  tight. 

Automobiles  use  double  pneumatic  tires.  The  double  pneu- 
matic automobile  tire  consists  of  a  rubber  inner  tube  to  be  in- 
flated and  a  casing,  made  up  of  rubber  and  canvas  fabric,  to 
protect  the  inner  tube  from  wear.  Two  types  of  casings  are 
used.  They  are  known  as  the  straight  side  and  the  clincher, 
depending  upon  the  method  of  holding  the  casing  in  the  rim. 

Carburetors. — Automobile  carburetors  have  been  illustrated 
and  described  in  Chapter  XIII. 

Ignition. — The  jump  spark  electric  ignition  system  is  employed. 
Most  modern  automobiles  employ  a  high-tension  distributor 
system  of  ignition,  using  batteries  as  the  source  of  current.     Fig. 


286        STEAM  AND  GAS  POWER  ENGINEERING 

220  illustrates  the  wiring  diagram  of  the  Atwater  Kent  high- 
tension  distributor  system,  which  is  operated  with  a  storage 
battery,  and  includes  the  following: 

1.  A  non-vibrator  type  of  induction  coil  with  primary  winding, 
secondary  winding,  and  electric  condenser.  This  type  of  induc- 
tion coil  produces  only  a  single  spark  as  the  circuit  is  made  and 
broken  only  once.     It  is  known  as  a  unisparker. 

2.  A  timer  or  contact-maker  in  the  primary  circuit.  The 
timer  is  constructed  so  that  the  length  of  contact  is  independent 
of  the  engine  speed. 

3.  A  high-tension  distributor  with  as  many  contact  points 
as  there  are  cylinders. 


DISTRIBUTOR 


1 — MAArllito" 


GROUND 


CONTACT  MAKER 

Fig.  220. — Wiring  diagram  of  the  Atwater  Kent  system. 

4.  A  governor  which  automatically  advances  the  spark 
within  certain  limits  as  the  speed  increases. 

The  automatic  spark-advance  mechanism,  the  contact  maker, 
and  the  distributor  are  all  carried  on  one  vertical  shaft.  The 
point  of  ignition  can  also  be  hand-controlled  by  turning  a  sleeve 
beneath  the  timer. 

The  Atwater  Kent  system  works  on  the  open  circuit  principle 
and  there  is  no  danger  of  running  down  the  batteries  by  leaving 
a  switch  closed. 

Fig.  221  illustrates  the  Delco  system.  This  system  includes 
starting,  generating,  ignition,  and  lighting  systems,  all  com- 
bined in  one.  A  motor-generator  set  performs  the  function  of 
cranking  the  engine  and  of  supplying  electrical  current  for  igni- 


AUTOMOBILES,  TRUCKS  AND  TRACTORS       287 

tion,  lighting,  sounding  the  horn,  and  charging  the  storage  battery. 
The  motor-generator  consists  of  a  dynamo  with  two  field  windings, 
and  two  windings  on  the  armature  with  the  commutators  and 
corresponding  sets  of  brushes.     This  construction  is  made  in 


order  that  the  machine  may  work  both  as  a  starting  motor  and 
as  a  generator.  The  ignition  apparatus  is  incorporated  in  the 
forward  end  of  the  motor-generator.  A  combination  switch  is 
used  for  the  purpose  of  controlling  the  lights,  the  ignition,  and 
the  circuit  between  the  electrical  generator  and  the  storage 
battery. 


288       STEAM  AND  GAS  POWER  ENGINEERING 

For  ignition  the  Delco  system  employs  a  non-vibrator  type  of 
induction  coil  with  a  timer  in  the  primary  circuit,  and  a  distribu- 
tor. A  governor  for  automatic  spark  advance  similar  to  that 
of  the  At  water  Kent,  but  of  different  design  is  employed.  In 
Fig.  221,  if  button  B  is  pulled  out,  the  current  for  ignition  will 
be  supplied  by  the  dry  cells.  By  pulling  button  M,  current  will  be 
supplied  through  wire  A,  if  the  generator  is  in  operation,  or  by 
the  storage  battery  through  wire  B. 

Automobile  Starting  Systems. — Automobile  motors  are  started 
by  hand  cranking  or  by  some  automatic  starting  device.  Before 
the  motor  is  cranked  the  carburetor  throttle  lever  on  the  steering 
wheel  should  be  moved  to  a  position  where  the  throttle  is  open. 
The  spark  should  be  shifted  to  the  retard  position,  as  failure  to 
do  this  may  result  in  the  engine  kicking  back  on  account  of 
back  firing.     The  gears  should  be  placed  into  neutral  position. 

In  cranking  by  hand,  the  crank  should  be  pushed  in 
as  far  as  possible  and  turned  in  the  clockwise  direction 
until  it  catches.  The  motor  should  start  if  the  crank  is  given  a 
quarter  or  a  half  turn  in  the  right  direction.  In  cranking  an 
engine,  always  set  the  crank  so  as  to  pull  up.  One  should  not 
bear  down  on  the  crank. 

Electric  starting  devices  are  usually  employed  in  modern 
automobiles.  An  electric  self-starter  consists  of  an  electric 
generator  for  furnishing  electricity,  a  storage  battery,  and  an 
electric  motor  to  crank  the  engine.  The  electric  starting  system 
is  also  supplied  with  switches  for  the  purpose  of  controlling  the 
supply  of  current;  with  protective  devices  such  as  fuses  or  cir- 
cuit-breakers to  prevent  the  discharging  of  the  storage  battery  or 
damage  to  the  coils,  motor,  or  lamps;  with  an  electric  regulator 
to  maintain  constant  voltage  for  the  various  speeds  of  the  engine ; 
and  with  electric  meters  for  the  purpose  of  showing  the  amount 
of  current  supplied  by  the  generator  to  the  storage  battery  and 
for  indicating  how  much  current  is  being  supplied  by  the  battery 
for  ignition  and  lighting. 

Electric  starters  are  built  in  the  single-unit,  the  two-unit,  or 
the  three-unit  system.  In  the  single-unit  system  the  generator 
and  motor  are  in  one  unit  and  this  motor-generator  is  used  for 
cranking  the  engine,  for  charging  the  storage  battery,  and  for 


AUTOMOBILES,  TRUCKS  AND  TRACTORS       289 

furnishing  current  to  be  used  for  operating  the  engine  ignition 
system  and  for  the  automobile  lights.  In  the  two-unit  system 
a  separate  motor,  which  receives  its  current  supply  from  the 
storage  battery,  is  used  for  cranking  the  engine.  The  electric 
generator  supplies  current  for  charging  the  storage  battery  and 
also  for  ignition  and  lighting.  In  the  three-unit  system  a  magneto 
furnishes  current  for  the  engine  ignition  system;  a  separate  direct- 
current  motor,  supplied  with  current  from  a  storage  battery,  is 
used  for  cranking;  while  the  electric  generator  is  used  only  for 
charging  the  storage  battery  and  for  operating  the  lights. 

Mechanical  starters  are  also  used  to  a  limited  extent  on 
small  cars,  but  have  been  largely  superseded  by  electric 
starters.  Some  mechanical  starters  utilize  springs,  which 
when  released  revolve  the  engine  crankshaft.  Other  mechani- 
cal starters  depend  for  their  action  upon  a  clamp,  but  are 
mainly  hand-cranking  devices  with  the  driver  remaining  in  the 
seat.  Safety  cranks  are  also  manufactured  for  the  purpose  of 
reducing  the  danger  of  an  accident  in  starting. 

Automobile  Lighting. — Electric  lights  are  used  almost  exclu- 
sively on  modern  automobiles.  The  electricity  for  illumination 
is  usually  secured  from  a  storage  battery.  In  the  cars  with 
electric  starters,  the  storage  battery  is  recharged  from  the  gen- 
erator; in  other  cases  the  battery  is  recharged  from  an  outside 
source.  In  some  automobiles,  notably  the  Ford,  alternating- 
current  magnetos  furnish  lighting  current  while  the  car  is  in 
motion. 

A  car  lighted  with  a  battery  charged  from  an  outside  source  is 
equipped  with  a  storage  battery  of  80  to  100  ampere-hour  capac- 
ity which  supplies  current  for  illumination  and  for  blowing 
the  horn.  This  lighting  storage  battery  is  usually  not  used  for 
engine  ignition,  unless  the  car  is  equipped  with  a  dynamo  to  re- 
charge the  battery.  When  the  storage  battery  is  used  for  light- 
ing, ignition,  and  starting,  its  capacity  should  be  at  least  90 
ampere-hours. 

Management  of  Automobiles. — Before  an  attempt  is  made  to 
start  an  automobile  the  operator  should  be  certain  that  the  fuel 
tank  has  sufficient  gasoline,  that  the  gasoline  valve  from  the  tank 
to  the  carburetor  is  open,  that  the  lubricating  system  is  in  good 
working  order,  that  the  radiator  is  filled  with  clean  water,  and 


290        STEAM  AND  GAS  POWER  ENGINEERING 

that  the  engine  ignition  system  is  working  properly.  The  trans- 
mission system  should  be  thrown  into  neutral  position,  the  spark 
lever  should  be  shifted  to  the  retarded  position,  and  the  carbu- 
retor throttle  should  be  partly  opened  before  the  engine  is  cranked. 
The  rules  given  in  the  discussion  of  starting  systems  should  be 
followed  in  starting  an  automobile  by  hand  cranking.  With 
electric  self-starters,  the  starting  pedal  is  pushed  forward  or 
down  as  far  as  it  will  go  and  held  until  the  engine  starts.  As  soon 
as  the  engine  starts  the  foot  should  be  removed  from  the  starter 
pedal. 

Easy  starting  may  be  obtained  by  throttling  the  air  just  as 
the  engine  stops,  thus  leaving  a  rich  mixture  in  the  cylinders. 
In  extremely  cold  weather,  or  after  prolonged  standing  of  the 
car,  it  may  be  necessary  to  prime  the  carburetor  or  even  to 
inject  gasoline  into  the  cylinder  through  each  of  the  priming  cups. 

When  the  engine  starts,  the  spark  lever  should  be  advanced. 
To  start  the  car,  the  emergency  brake  is  released,  the  clutch  is 
disengaged,  while  the  transmission  gears  are  thrown  into  low 
gear  forward,  and  the  foot  accelerator  and  the  spark  lever  are 
operated  to  take  care  of  the  increased  load  on  the  car.  In  chang- 
ing from  low  to  intermediate  and  to  high  speed,  the  clutch  is 
thrown  out,  the  gears  are  shifted,  the  clutch  is  thrown  in  mesh, 
and  the  throttle,  or  foot  accelerator,  is  adjusted  for  proper 
operation. 

To  stop  an  automobile,  the  motor  is  slowed  down  by  removing 
the  foot  from  the  accelerator,  the  clutch  is  disengaged,  the  serv- 
ice brake  is  operated  so  that  the  car  comes  to  a  gradual  stop, 
and  the  transmission  gears  are  shifted  into  neutral  position. 

To  stop  quickly  the  operator  presses  on  both  pedals,  releasing 
the  clutch  and  applying  the  service  brake,  while  applying  also 
the  hand  emergency  brake. 

To  reverse,  the  car  is  stopped,  the  reverse  gear  is  shifted,  and  the 
clutch  is  thrown  in  slowly. 

Details  concerning  the  care  of  a  car  are  given  in  manufacturers' 
instruction  books  and  will  not  be  repeated  here. 

An  automobile  engine  will  smoke  if  too  much  lubricating  oil 
is  used,  if  the  lubricating  oil  is  of  poor  quality,  if  the  piston  rings 
are  worn  or  broken,  or  if  the  mixture  of  air  and  fuel  is  incorrect. 

Engine  hissing  may  be  produced  by  loose  or  broken  spark 


AUTOMOBILES,  TRUCKS  AND  TRACTORS       291 

plugs,  by  leaving  priming  or  relief  cocks  open,  by  having  exhaust 
pipe  loosely  connected,  or  by  leaky  gaskets  or  intake  manifolds. 

Irregular  action  of  the  automobile  engine  may  be  due  to  incor- 
rect fuel  mixture,  poor  wiring  such  as  defective  insulation  or 
defective  connections,  carbon  deposits,  poor  fuel,  or  defects  in 
carburetor,  magnetos,  spark  plugs,  or  mechanism. 

Misfiring  is  often  due  to  carbon  deposits  on  the  spark  plug. 
Overheating  of  the  engine  may  be  due  to  incorrect  valve  or  spark 
timing,  defective  water  circulation,  clogged  radiator,  or  a  lack  of 
proper  lubrication  Engine  knocks  are  due  to  rich  mixture,  too 
much  spark  advance,  carbon  deposits  in  the  cylinder,  loose  or 
worn  bearings,  loose  flywheel,  or  lack  of  lubrication. 

Trucks 

Most  of  the  essential  parts  of  a  truck  are  similar  to  those  of  an 
automobile,  but  are  usually  heavier  to  stand  the  greater  strains 
imposed  by  the  conditions  under  which  a  truck  operates. 

Power  Plants  for  Trucks. — The  truck  power  plant  is  usually  a 
four-cylinder  vertical  poppet  valve  type  of  internal-combustion 
engine,  which  operates  on  the  Otto  four-stroke  cycle.  Six-cylin- 
der engines  are  employed  to  a  limited  extent  in  trucks. 

A  standard  type  of  float-feed  carburetor  is  used,  such  as  the 
Stromberg  plain  tube  or  the  Zenith.  Some  trucks  are  equipped 
with  special  carburetors,  such  as  the  White,  the  Packard,  or  the 
Pierce  Arrow. 

Truck  motors  are  cooled  with  the  forced  water  circulation  sys- 
tem and  are  usually  provided  with  tubular  radiators,  in  which 
the  upper  and  lower  tanks  are  connected  by  a  series  of  tubes 
through  which  the  water  passes.  Some  of  the  lighter  trucks 
are  equipped  with  cellular  radiators  similar  to  those  used  on 
automobiles. 

The  jump  spark  system  of  ignition  is  employed.  In  some 
makes  of  trucks,  batteries  are  used  for  furnishing  current  when 
starting  and  magnetos  supply  electricity  for  ignition  after  the 
motor  has  attained  normal  speed.  This  is  called  the  dual  sys- 
tem. Most  trucks  are  equipped  with  a  high-tension  magneto. 
In  some  cases  trucks  are  provided  with  two  independent  ignition 
systems,  including  a  high-tension  magneto  and  a  distributor. 


292       STEAM  AND  GAS  POWER  ENGINEERING 

Power  Transmission  Systems  for  Trucks. — The  power  trans- 
mission systems  of  trucks  and  of  automobiles  include  the  same 
elements. 

Some  trucks  employ  a  dry  multiple  disc  clutch  and  others  use 
a  wet  multiple  disc  clutch.  Dry  or  wet  single-plate  clutches  are 
also  used  for  trucks.  The  principle  of  operation  of  the  plate 
clutch  is  similar  to  that  of  the  cone  clutch.  The  friction  plate  is 
independent  of  the  flywheel  and  of  the  housing  and  a  spring 
holds  the  friction  surfaces  in  contact.  The  friction  surfaces  are 
separated  by  depressing  a  foot  pedal. 


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Fig.  222. — Truck  transmission. 

The  transmission  of  a  truck  is  usually  of  the  selective  type  and 
includes  three  speeds  forward  and  one  reverse.  Some  trucks  em- 
ploy a  four-speed  transmission  system.  Such  trucks  have  direct 
drive  on  the  fourth  speed  and  three  lower  gear  ratios.  To  reduce 
the  danger  of  stripping  gear  teeth  the  gears  of  the  counter  shaft 
and  main  shaft  of  the  transmissions  for  heavy  trucks  are  placed 
permanently  in  mesh,  the  drive  being  obtained  by  the  use  of 
shifting  forks  or  clutches.  A  typical  transmission  for  a  heavy 
truck  is  shown  in  Fig.  222. 

The  propeller  shaft  carries  the  power  from  the  transmission 
through  the  universal  joints  to  the  rear  axles.     The  power  from 


AUTOMOBILES,  TRUCKS  AND  TRACTORS       293 

the  propeller  shaft  to  the  rear  axle  is  transmitted  either  by  shaft 
or  by  chain  drive. 

The  shaft  drive  is  the  most  common  for  trucks  as  well  as  for 
automobiles.  The  shaft  drive  transmits  the  power  to  the  differen- 
tial, which  is  placed  on  the  rear  axle  through  bevel,  helical,  or 
worm  gears.  The  bevel  gear  drive  is  seldom  employed  for  trucks. 
The  helical  or  spiral  bevel  gear  drive  is  more  satisfactory,  as  two 
or  more  teeth  are  in  mesh  at  one  time,  reducing  irregularity 
in  wear.  The  worm  gear  drive  is  particularly  well  suited  for 
trucks,  on  account  of  the  large  gear  reduction  which  this  drive 
makes  possible.  A  large  differential  gear  reduction  decreases 
the  torque  required  to  drive  the  rear  wheels. 

For  heavy  trucks  chains  are  often  used  for  the  final  drive  in 
order  to  obtain  the  greatest  possible  speed  reduction.  In  such 
trucks  the  differential  is  not  placed  on  the  rear  axle,  but  is  con- 
tained in  the  same  housing  with  the  transmission.  From  the 
differential  the  power  is  transmitted  to  jack  shafts,  which  drive 
the  rear  wheels  by  means  of  chains. 

Some  trucks  are  constructed  so  that  they  drive  and  steer  with 
four  wheels.  In  such  cases  the  power  from  the  transmission  is 
transmitted  to  two  differentials.  One  differential  serves  to  trans- 
mit the  power  to  the  front  wheels  and  the  other  to  the  rear  wheels. 

The  differential  of  the  truck  has  the  same  function  as  that  of 
the  automobile  and  permits  the  drive- wheels  to  revolve  at  differ- 
ent speeds  without  interfering  with  the  operation  of  the  truck. 

Tractors 

Essential  Parts  of  a  Tractor. — A  tractor  consists  of  the  fol- 
lowing essential  parts: 

1.  Power  Plant. — This  in  the  case  of  a  steam  tractor  includes 
a  steam  engine,  a  boiler,  a  pump  or  injector,  steam  and  feed 
water  piping,  fuel  hopper,  water  storage,  and  the  ordinary  steam 
power  plant  accessories.  Gas  tractors  employ  an  internal  com- 
bustion motor  burning  gasoline,  kerosene,  or  some  heavier  oil. 

2.  Speed  Redaction  Gears. — A  train  of  gears  must  be  interposed 
between  the  motor  and  the  drive  wheels  in  order  that  the  tractor 
may  be  propelled  at  a  very  low  speed. 

J  3.  Reversing  Mechanism. — A  steam  tractor  is  reversed  by  a 
Stephenson  link  motion  similar  to  that  used  for  reversing  loco- 


294        STEAM  AND  GAS  POWER  ENGINEERING 

motives  or  by  some  form  of  single  eccentric  radial  valve  gear. 
Gas  tractors  employ  a  train  of  gears. 

4.  Steering  Mechanism. — -Steering  is  usually  accomplished  by 
turning  the  front  axle. 

5.  Friction  Clutch. — A  friction  clutch  is  necessary  for  the  pur- 
pose of  disengaging  the  motor  from  the  propelling  gear.  The 
expanding  cone  and  the  expanding  shoe  clutches  are  used  in 
addition  to  those  explained.  Fig.  223  illustrates  an  expanding 
shoe  clutch. 


Fig.  223.— Tractor  clutch. 


6.  Differential.— The  differential  (Fig.  224)  is  similar  to  that 
used  on  trucks  and  its  function  is  to  allow  one  drive  wheel  to 
revolve  independently  of  the  other. 

7.  Tractor  Frame. — The  frame  supports  the  various  parts  and 
keeps  them  in  proper  alignment. 

8.  Drive  Wheels  and  Steering  Wheels. — Usually  the  two  rear 
wheels  are  the  drive  wheels  and  the  two  front  wheels  are  used 
for  steering.  Some  tractors  employ  a  drum  for  driving,  several 
makes  are  constructed  so  that  the  front  wheels  are  the  driving 
wheels,  and  in  other  makes  all  four  wheels  drive.  Tractors 
are  also  built  on  the  "  Caterpillar"  principle  and  employ  a  crawler 
instead  of  a  wheel  or  drum. 


AUTOMOBILES,  TRUCKS  AND  TRACTORS       295 

Steam  Tractors. — The  steam  tractor,  or  traction  engine,  is 
usually  equipped  with  an  internally  fired  boiler.  Some  builders 
use  the  return  flue  type,  others  the  direct  flue  or  locomotive  type. 

Coal,  lignite,  wood,  straw,  or  crude  oil  are  used  as  fuels  for 
steam  tractors. 

The  feed  water  is  delivered  to  the  boiler  by  an  injector,  a  direct- 
acting  steam  pump,  a  cross-head  pump,  or  a  gear-driven  pump. 
Some  tractors  employ  two  independent  methods  for  feeding  water 
to  the  boiler. 


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Fig.  224. — Tractor  differential. 


Feed-water  heaters  are  used  in  connection  with  the  better  types 
of  steam  traction  engines. 

A  simple  type  of  slide  valve  engine  is  employed.  Some  tractors 
are  provided  with  double-cylinder  engines.  Compound  engines 
are  also  used  to  some  extent. 

Gas  Tractors. — The  use  of  the  gas  tractor  has  been  increasing 
much  more  rapidly  than  that  of  the  steam  tractor.  Gas  tractors 
are  made  in  many  different  sizes,  prices,  and  special  designs 
suitable  for  various  uses.  A  gas  tractor  can  be  started  much  more 
quickly  than  one  propelled  by  a  steam  engine  and  requires  less 
attention. 


296        STEAM  AND  GAS  POWER  ENGINEERING 

The  motors  of  gas  traction  engines  usually  operate  on  the  Otto 
four-stroke  cycle  and  use  gasoline  or  kerosene  for  fuel.  The 
motors  are  either  vertical  or  horizontal  and  operate  at  moderate 
speeds  as  compared  with  the  motors  used  on  automobiles.  The 
vertical  motor  resembles  the  truck  motor,  but  is  usually  heavier. 
Fig.  225  illustrates  the  type  of  motor  commonly  used  on  gas 
tractors. 

Float-feed  carburetors  of  the  single  jet  automobile  type  are 
generally  used. 


Fig.  225. — Four-cylinder  tractor  motor 


Nearly  all  tractors  employ  the  jump-spark  ignition  system. 
The  ignition  system  differs  from  that  of  automobiles  in  that 
magnetos  are  commonly  employed. 

Rating  of  Tractors. — Two  ratings  are  usually  given  to  tractors. 
One  is  in  brake  or  belt  horsepower.  This  indicates  the  power 
developed  at  the  shaft  of  the  engine,  which  can  be  used  for  driv- 
ing various  machines  by  means  of  belt  drive.  The  other  rating 
is  the  tractive  or  draw-bar  horsepower.  The  tractive  horse- 
power is  usually  one-half  to  two-thirds  of  the  brake  horsepower, 


AUTOMOBILES,  TRUCKS  AND  TRACTORS       297 

depending  upon  the  transmission  gearing  and  on  the  character 
of  the  ground  over  which  the  tractor  must  be  propelled. 

Care  of  Trucks  and  Tractors. — The  general  directions  given 
concerning  the  care  of  an  automobile  apply  to  the  truck  and 
tractor.  Wearing  surfaces  must  be  kept  well  lubricated  and  lost 
motion  in  bearings  must  be  avoided. 

The  steering  mechanism  of  the  tractor  is  less  sensitive  than 
that  of  the  automobile  or  even  of  the  truck  on  account  of  its 
slower  speed  and  the  lower  gear  ratio  of  the  steering  wheel. 

Overloading  a  truck  or  a  tractor  is  a  serious  mistake.  The  life 
and  usefulness  of  any  piece  of  machinery  is  increased  by  proper 
housing  and  systematic  upkeep.  The  lubricating  system  of  the 
motor  should  be  examined  daily.  Frequent  inspection  should 
be  made  to  determine  the  condition  of  the  spark  plugs,  the  align- 
ment of  the  wheels,  condition  of  the  brakes,  clutch,  springs,  rods, 
cylinders,  and  bearings.  Valves  should  seat  properly  and  should 
be  correctly  timed. 

Problems 

1.  Make  clear  sketches  showing  the  mechanism  of  an  automobile  steering 
gear. 

2.  Make  a  clear  sketch  of  a  universal  joint. 

3.  Prepare  a  table  showing  the  important  differences  in  the  specifications 
of  automobiles  and  of  trucks. 


INDEX 


Air  brakes,  270 

Air-cooled  gas  engine,  201 

Air  pump,  dry,  174 

Air  pump,  wet,  173 

Air  required  for  combustion,  18 

Acohol,  denatured,  218 

Alcohol  fuel,  217 

Angle  valve,  88 

Anthracite  coal,  14 

Ash  handling  machinery,  81 

Automobile  axles,  284 

brakes,  285 

clutch,  279 

control  system,  284 

cooling  systems,  275 

differential,  282 

electric,  273 

gasoline,  273 

ignition  systems,  285 

lighting,  289 

lubrication,  276 

management,  289 

motors,  274 

parts,  274 

starting  systems,  288 

steam,  273 

steering  system,  284 

tires,  285 

transmissions,  280 

types,  273 

valves,  278 

wheels,  285 
Axles,  automobile,  284 


B 


Babcock  &  Wilcox  boiler,  45 
Balanced  valves,  98 
Batteries,  electric,  241 

primary,  242 

storage,  242 


Bearings,  127 
Benzol,  218 
Blast  furnace  gas,  219 
Blow-off  valve,  88 
Bituminous  coal,  15 
Boiler,  capacity  of,  53 

classification  of,  35 

efficiency  of,  53 

management,  56 
Boiler  furnaces,  52 
Boiler,  heating  surface,  51 

horizontal  tubular,  36 

locomotive,  39 

marine,  39 

marine  water  tube,  49 

plain  cylindrical,  35 

settings,  52 

staying,  51 

vertical  fire  tube,  41 

water  tube,  43 
Boiler  with  dome,  37 
Brake  horse  power,  122,  256 
Branca  turbine,  138 


Calorimeter,  coal,  11 

gas,  212 
Capacity  of  boilers.  53 
Carburetion,  principles  of,  228 
Carburetors,  float  feed,  229 

Holley,  235 

kerosene,  236 

Kingston,  230 

Marvel,  231 

Stewart,  232 

Stromberg,  233 

Zenith,  235 
Check  valve,  88 
Chemistry  of  combustion,  17 
Chimneys,  72 

capacity  of,  73 

draft,  72 
299 


300 


INDEX 


Clutch,  automobile,  279 

cone,  279 

disc,  279 
Clutch,  truck,  292 
Coal,  anthracite,  16 
Coal  as  fuel,  13,  14,  15 
Coal,  bituminous,  15 
Coal  calorimeter,  11 
Coal  handling  machinery,  81 
Coke-oven  gas,  219 
Combustion,  17 

Compound  impulse  turbines,  143 
Compound  steam  engine,  107 
Compression   pressures   for   various 
internal  combustion  engine 
fuels,  195 
Condenser,  barometric,  168 

ejector,  170 

jet,  167 

principle  of,  164 

surface,  171 

types,  166 
Conveyors  for  coal  and  ashes,  81 
Cooling  ponds,  177 
Cooling  towers,  177 
Crank  shaft,  92 

Cross  compound  steam  engine,  109 
Crude  oil,  217 

Crude  petroleum  distillates,  214 
Curtis  steam  turbine,  150 


Dead  center,  92 

DeLaval  simple  impulse  turbine,  138 

Diesel  internal  combustion  engine, 

198 
Differentials  for  automobiles,  282 
Distillates  of  petroleum,  214 
Distributor  system,  250 
Draft,  artificial,  74 

forced,  74 

gages,  185 

induced,  75 

natural,  72 
Dynamo,  ignition,  246 
Dynamometers,  189 


E 


Eccentric,  93 

Economizer,  70 

Economy  of  steam  engines,  129 

Economy  of  steam  turbines,  161 

Edison  storage  battery,  245 

Efficiency,  mechanical,  123 

Efficiency  of  boilers,  53 

Electric  batteries,  241 

Energy  of  steam,  142 

Energy,  source  of,  2 

Engine.     See  Steam  engine  or  Internal 

combustion  engine. 
Engine  condensing,  106 
Engine,  Corliss,  100 

non-condensing,  107 

reversing,  102 
Erecting  pipe,  86 
Exhaust  head,  181 
Exhaust  steam  turbines,  160 
Expansion  joints,  86 
Expansion  of  piping,  85 


Feed  pumps,  76 
Feed  water  heater,  68 

closed  type,  70 

open  type,  69 
Feed  water  heating,  economy  of,  68 
Fire   tube  boiler  settings,    36,    37, 

38 
Firing,  55 
Fittings,  flanged,  83 

screwed,  38 
Flue  gas  analysis,  19 
Flywheel,  93 
Four  stroke  cycle,  192 
Friction  horsepower,  123 
Fuel,  flash  point  of,  214 
Fuel  gases,  218 
Fuel,  selection  of,  213 
Fuel,  specific  gravity  of,  213 
Fuels  for  internal  combustion  en- 
gines, 211 
Fuels  for  steam  power,  10 


INDEX 


301 


Fuels,  heating  value  of,  10,  212 

liquid,  211 

proximate  analysis,  12 
Furnaces  for  boilers,  52 
Fusible  plug,  91 


History  of  the  steam  turbine,  137 
Hit-and-miss  governing,  252 
Horizontal  tubular  boiler,  36 
Horse  power,  definition  of,  114 
Horse  power,  indicated,  114 
Hot  air  engine,  3,  4 


Gage,  steam,  89 
Gas  calorimeter,  212 
Gas  engine.     See   Internal   combus- 
tion engine. 
Gas  engine  governor,  251 
Gas  engine  indicator  diagram,    195 
Gas  engine,  starting  of,  207 
Gasoline,  216 
Gasoline,  casing  head,  216 

cracked,  216 

straight  refinery,  216 
Gas  producers,  220 

classification  of,  222 

combination,  223 

details  of,  220 

down  draft,  224 

operation,  226 

pressure,  223 

rating  of,  226 

suction,  222 

testing,  258 
Gate  valve,  87 
Globe  valve,  87 

Governors  for  gas  engines,  252 
Governors  for  steam  engines,    124, 

125,  126 
Grates  for  furnaces,  80 
Grate,  shaking  type,  81 


H 


Heat  consumption  of  gas  engine,  256 
Heating  surface  of  boilers,  51 
Heating  value  of  fuels,  10 
Heine  boiler,  45 
Hero's  turbine,  137 
History  of  internal  combustion  en- 
gine, 191 
History  of  the  steam  engine,  94 


Igniter,  hammer  brake,  238 
Igniter,  wipe-spark,  238 
Ignition,  Atwater  Kent,  286 
Ignition,  Delco,  286 
Ignition  dynamo,  246 
Ignition,  electric,  237 

hot  tube,  236 

jump  spark,  239 

make-and-break,  237 
Ignition  systems,  236 
Indicated  horse  power  of  gas  engines, 

256 
Indicator  card,  118 
Indicator  for  steam  engines,  155 
Indicator  reducing  motions,  117 
Indicator  reducing  wheel,  118 
Inductance  coil,  237 
Induction  coil,  239 
Injectors,  79 
Installation  of  internal  combustion 

engines,  206 
Installation  of  steam  engines,  130 
Installation  of  steam  turbines,  161 
Internal  combustion  engine,  191 

care  of,  207,  208,  209 

compression  pressures,  195 

details,  200 

history,  191 

losses,  206 

operation,  207,  208,  209 

parts,  193 

timing,  208,  209 


Kerosene,  217 
Kerr  steam  turbine, 


147 


302 


INDEX 


Lead  of  a  valve,  97 
Lead  storage  battery,  244 
Lenoir  engine,  192 
Lignite,  15 

Locomobile,  steam,  109 
Locomotive  boiler,  39 

classification,  274 

compound,  266 

details,  260 

development,  266 

history  of,  264 
Locomotive  stoker,  268 
Locomotive  superheater,  267 
Losses  in  steam  engines,  95 
Lubrication,  automobile,  276 
Lubricators  for  steam  engines,  128, 
129 

M 

Magneto,  246 

high  tension,  248 

inductor  type,  247 

low  tension,  247 
Management  of  boilers,  56 
Marine  boiler,  39 
Marine  water  tube  boiler,  49 
Materials  for  boilers,  50 
Mechanical  efficiency,  123 
Mixer  valves,  228 
Motor,  definition  of,  1 
Motor,  electric,  3 
Muffler,  254 

N 

Natural  gas,  219 
Newcomer  engine,  95 


Oil,  crude,  217 

Oil  engines,  204 

Oil  engine,  semi- Diesel  type,  205 

Oil  fuel  for  steam  making,  16 

Orsat  apparatus,  19 

Otto  cycle,  192 


Parker  boiler,  48 

Parsons  steam  turbine,  155 

Parts  of  a  steam  engine,  92,  93,  94 

Petroleum  distillates,  214 

Pipe  bushing,  85 

Pipe  cap,  85 

Pipe  couplings,  84 

Pipe  covering,  86 

Pipe,  cross,  85 

Pipe,  erecting,  85 

Pipe,  double  extra  heavy,  83 

elbow,  85 

extra  heavy,  83 
Pipe  fittings,  83,  84,  85 
Pipe  flange,  85 
Pipe  sizes,  83 
Pipe,  standard,  83 
Pipe  tee,  85 
Pipe  unions,  84 
Piping  grades,  83 
Planimeter,  120 
Plain  slide  valve,  96 
Plain  slide  valve  types,  98 
Plug,  fusible,  91 

Power,   amount  used  for  manufac- 
turing, 5 
Power,  development  of,  1 
Power  from  indicator  cards,  119 
Power,  measurement  of,  189 
Preignition,  209 
Primary  batteries,  242 
Producer  gas,  219 
Producers,  gas,  220 
Prony  brake,  123 
Pump,  circulating,  175 
Pump,  direct  acting,  77 
Pumps,  duty  of,  80 

vacuum,  171 
Pyrometers,  186 


B 


Radial  valve  gears,  106 
Radiation  loss,  96 
Rateau  turbine,  143 


INDEX 


303 


Reaction  turbine,  154 
Reversing  steam  engine,  102 


S 


Safety  valve,  88 

lever,  88 

pop,  89 
Separating  calorimeter,  32 
Separator,  oil,  180 
Separators,  steam,  179 
Settings  for  boilers,  52 
Shale  oil,  218 
Solar  motor,  3,  4 
Spark  plug,  240 
Speed  measurement,  189 
Spiro  turbine,  159 
Spray  ponds,  177 
Steam  calorimeters,  31,  32 
Steam  chest,  92 
Steam,  energy  of,  142 
Steam  engine,  92 

care  of,  130 

compound,  107 

connecting  rod,  127 

cross  head,  127 

Corliss,  100 

details,  126,  127 

economy,  129 

governor,  124,  125,  126 

history,  94 

indicator,  115 

installation,  130,  131 

losses,  95 

operation,  131,  132,  133,  134 

parts,  92,  93,  94 

piston,  126 

Uniflow,  102 
Steam  gage,  89 
Steam  generation,  21 
Steam  locomobile,  109 
Steam  meters,  187 
Steam  power  plants,  5,  6,  7,  8 
Steam  power  plant  testing,  182 
Steam,  quality  of,  22,  30 
Steam  separators,  179 
Steam  tables,  23-28 


Steam  trap,  90 

Steam,  velocity  of,  142 

Steam  turbines,  135 

Steam  turbine,  Westinghouse,   150, 

158 
Steam  turbine,  double-flow,  158 

advantages  of,  136 

applications,  160 

blading,  152,  158 

care  of,  161 

Curtis,  150 

DeLaval,  138,  148 

economy,  161 

exhaust  types,  160 

governors,  140,  154,  156 

history  of,  137 

impulse-reaction  type,  158 

Kerr,  147 

nozzles,  140,  151 

Parsons,  155 

Rateau,  143 

Reaction  type,  154 

Spiro,  159 

Sturtevant,  150 

Terry,  149 

Westinghouse,  150,  158 
Steam,  velocity  of,  142 
Stephenson  link  motion,  105 
Stirling  boiler,  45 
Stoker,  American  underfeed,  68 

Chain  grate,  63 

classification,  63 

economics  of,  63 

field  for,  62 

inclined  grate,  64 

Jones  underfeed,  66 

Murphy,  65 

Roney,  65 

Westinghouse,  68 

underfeed,  66 
Storage  batteries,  242 
Storage  battery,  lead  type,  244 

Edison,  245 
Sun,  source  of  energy,  2 
Superheater,  attached  type,  58 

Babcock  &  Wilcox,  60 

Foster,  62 


304 


INDEX 


Superheater,  Heine,  61 

independently  fired,  58 
overheating,  59 
Stirling,  60 
types,  58 


Tandem    compound   steam    engine, 

108 
Terry  steam  turbine,  149 
Throttling  calorimeter,  31 
Timer,  249 
Tractor,  care  of,  296 
Tractor  details,  293 
Tractor  motors,  295 
Tractors,  gas,  295 

rating,  296 

steam,  295 
Transmission,  automobile,  280 

planetary,  281 

selective,  281 
Trap,  steam,  90 
Truck,  care  of,  296 

details  of,  291 

motor,  291 

power  plant,  291 

power  transmission,  292 
Turbine.  See  Steam  turbine. 
Two-stroke  cycle,  196 

U 

Uniflow  steam  engine,  102 
Union,  pipe,  84 
Unit  of  heat,  11 
Universal  joints,  283 


Valve,  poppet,  101,  278 

sleeve  type,  278 
Vertical  fire  tube  boiler,  41 
Vacuum  measurement,  165 
Valve,  safety,  88 
Valves,  87 

angle  type,  88 

balanced,  98 

blow  off,  88 

Corliss,  100 

double  ported,  99 

gate,  87 
Valve  gears,  radial,  106 
Valve,  globe,  87 

setting,  110,  111,  112,  113,  114 

setting  by  indicator,  121 
Valve  timing  of  gas  engines,  208 
Velocity  of  steam,  142 
Venturi  meter,  185 
Volatile  matter  in  fuel,  12 

W 

Walschaert  valve  gear,  106 

Water  column,  90 

Water  cooled  gas  engine,  201 

Water  glass,  90 

Water  tube  boiler,  43 

Watt  engine,  95 

Weir,  184 

Wickes  boiler,  47 

Windmill,  3,  4 

Wood  as  fuel,  13 


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